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linux/init/Kconfig
Mathieu Desnoyers 5b25b13ab0 sys_membarrier(): system-wide memory barrier (generic, x86) 
Here is an implementation of a new system call, sys_membarrier(), which
executes a memory barrier on all threads running on the system.  It is
implemented by calling synchronize_sched().  It can be used to
distribute the cost of user-space memory barriers asymmetrically by
transforming pairs of memory barriers into pairs consisting of
sys_membarrier() and a compiler barrier.  For synchronization primitives
that distinguish between read-side and write-side (e.g.  userspace RCU
[1], rwlocks), the read-side can be accelerated significantly by moving
the bulk of the memory barrier overhead to the write-side.

The existing applications of which I am aware that would be improved by
this system call are as follows:

* Through Userspace RCU library (http://urcu.so)
  - DNS server (Knot DNS) https://www.knot-dns.cz/
  - Network sniffer (http://netsniff-ng.org/)
  - Distributed object storage (https://sheepdog.github.io/sheepdog/)
  - User-space tracing (http://lttng.org)
  - Network storage system (https://www.gluster.org/)
  - Virtual routers (https://events.linuxfoundation.org/sites/events/files/slides/DPDK_RCU_0MQ.pdf)
  - Financial software (https://lkml.org/lkml/2015/3/23/189)

Those projects use RCU in userspace to increase read-side speed and
scalability compared to locking.  Especially in the case of RCU used by
libraries, sys_membarrier can speed up the read-side by moving the bulk of
the memory barrier cost to synchronize_rcu().

* Direct users of sys_membarrier
  - core dotnet garbage collector (https://github.com/dotnet/coreclr/issues/198)

Microsoft core dotnet GC developers are planning to use the mprotect()
side-effect of issuing memory barriers through IPIs as a way to implement
Windows FlushProcessWriteBuffers() on Linux.  They are referring to
sys_membarrier in their github thread, specifically stating that
sys_membarrier() is what they are looking for.

To explain the benefit of this scheme, let's introduce two example threads:

Thread A (non-frequent, e.g. executing liburcu synchronize_rcu())
Thread B (frequent, e.g. executing liburcu
rcu_read_lock()/rcu_read_unlock())

In a scheme where all smp_mb() in thread A are ordering memory accesses
with respect to smp_mb() present in Thread B, we can change each
smp_mb() within Thread A into calls to sys_membarrier() and each
smp_mb() within Thread B into compiler barriers "barrier()".

Before the change, we had, for each smp_mb() pairs:

Thread A                    Thread B
previous mem accesses       previous mem accesses
smp_mb()                    smp_mb()
following mem accesses      following mem accesses

After the change, these pairs become:

Thread A                    Thread B
prev mem accesses           prev mem accesses
sys_membarrier()            barrier()
follow mem accesses         follow mem accesses

As we can see, there are two possible scenarios: either Thread B memory
accesses do not happen concurrently with Thread A accesses (1), or they
do (2).

1) Non-concurrent Thread A vs Thread B accesses:

Thread A                    Thread B
prev mem accesses
sys_membarrier()
follow mem accesses
                            prev mem accesses
                            barrier()
                            follow mem accesses

In this case, thread B accesses will be weakly ordered. This is OK,
because at that point, thread A is not particularly interested in
ordering them with respect to its own accesses.

2) Concurrent Thread A vs Thread B accesses

Thread A                    Thread B
prev mem accesses           prev mem accesses
sys_membarrier()            barrier()
follow mem accesses         follow mem accesses

In this case, thread B accesses, which are ensured to be in program
order thanks to the compiler barrier, will be "upgraded" to full
smp_mb() by synchronize_sched().

* Benchmarks

On Intel Xeon E5405 (8 cores)
(one thread is calling sys_membarrier, the other 7 threads are busy
looping)

1000 non-expedited sys_membarrier calls in 33s =3D 33 milliseconds/call.

* User-space user of this system call: Userspace RCU library

Both the signal-based and the sys_membarrier userspace RCU schemes
permit us to remove the memory barrier from the userspace RCU
rcu_read_lock() and rcu_read_unlock() primitives, thus significantly
accelerating them. These memory barriers are replaced by compiler
barriers on the read-side, and all matching memory barriers on the
write-side are turned into an invocation of a memory barrier on all
active threads in the process. By letting the kernel perform this
synchronization rather than dumbly sending a signal to every process
threads (as we currently do), we diminish the number of unnecessary wake
ups and only issue the memory barriers on active threads. Non-running
threads do not need to execute such barrier anyway, because these are
implied by the scheduler context switches.

Results in liburcu:

Operations in 10s, 6 readers, 2 writers:

memory barriers in reader:    1701557485 reads, 2202847 writes
signal-based scheme:          9830061167 reads,    6700 writes
sys_membarrier:               9952759104 reads,     425 writes
sys_membarrier (dyn. check):  7970328887 reads,     425 writes

The dynamic sys_membarrier availability check adds some overhead to
the read-side compared to the signal-based scheme, but besides that,
sys_membarrier slightly outperforms the signal-based scheme. However,
this non-expedited sys_membarrier implementation has a much slower grace
period than signal and memory barrier schemes.

Besides diminishing the number of wake-ups, one major advantage of the
membarrier system call over the signal-based scheme is that it does not
need to reserve a signal. This plays much more nicely with libraries,
and with processes injected into for tracing purposes, for which we
cannot expect that signals will be unused by the application.

An expedited version of this system call can be added later on to speed
up the grace period. Its implementation will likely depend on reading
the cpu_curr()->mm without holding each CPU's rq lock.

This patch adds the system call to x86 and to asm-generic.

[1] http://urcu.so

membarrier(2) man page:

MEMBARRIER(2)              Linux Programmer's Manual             MEMBARRIER(2)

NAME
       membarrier - issue memory barriers on a set of threads

SYNOPSIS
       #include <linux/membarrier.h>

       int membarrier(int cmd, int flags);

DESCRIPTION
       The cmd argument is one of the following:

       MEMBARRIER_CMD_QUERY
              Query  the  set  of  supported commands. It returns a bitmask of
              supported commands.

       MEMBARRIER_CMD_SHARED
              Execute a memory barrier on all threads running on  the  system.
              Upon  return from system call, the caller thread is ensured that
              all running threads have passed through a state where all memory
              accesses  to  user-space  addresses  match program order between
              entry to and return from the system  call  (non-running  threads
              are de facto in such a state). This covers threads from all pro=E2=80=90
              cesses running on the system.  This command returns 0.

       The flags argument needs to be 0. For future extensions.

       All memory accesses performed  in  program  order  from  each  targeted
       thread is guaranteed to be ordered with respect to sys_membarrier(). If
       we use the semantic "barrier()" to represent a compiler barrier forcing
       memory  accesses  to  be performed in program order across the barrier,
       and smp_mb() to represent explicit memory barriers forcing full  memory
       ordering  across  the barrier, we have the following ordering table for
       each pair of barrier(), sys_membarrier() and smp_mb():

       The pair ordering is detailed as (O: ordered, X: not ordered):

                              barrier()   smp_mb() sys_membarrier()
              barrier()          X           X            O
              smp_mb()           X           O            O
              sys_membarrier()   O           O            O

RETURN VALUE
       On success, these system calls return zero.  On error, -1 is  returned,
       and errno is set appropriately. For a given command, with flags
       argument set to 0, this system call is guaranteed to always return the
       same value until reboot.

ERRORS
       ENOSYS System call is not implemented.

       EINVAL Invalid arguments.

Linux                             2015-04-15                     MEMBARRIER(2)

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Nicholas Miell <nmiell@comcast.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Pranith Kumar <bobby.prani@gmail.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-09-11 15:21:34 -07:00

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config ARCH
string
option env="ARCH"
config KERNELVERSION
string
option env="KERNELVERSION"
config DEFCONFIG_LIST
string
depends on !UML
option defconfig_list
default "/lib/modules/$UNAME_RELEASE/.config"
default "/etc/kernel-config"
default "/boot/config-$UNAME_RELEASE"
default "$ARCH_DEFCONFIG"
default "arch/$ARCH/defconfig"
config CONSTRUCTORS
bool
depends on !UML
config IRQ_WORK
bool
config BUILDTIME_EXTABLE_SORT
bool
menu "General setup"
config BROKEN
bool
config BROKEN_ON_SMP
bool
depends on BROKEN || !SMP
default y
config INIT_ENV_ARG_LIMIT
int
default 32 if !UML
default 128 if UML
help
Maximum of each of the number of arguments and environment
variables passed to init from the kernel command line.
config CROSS_COMPILE
string "Cross-compiler tool prefix"
help
Same as running 'make CROSS_COMPILE=prefix-' but stored for
default make runs in this kernel build directory. You don't
need to set this unless you want the configured kernel build
directory to select the cross-compiler automatically.
config COMPILE_TEST
bool "Compile also drivers which will not load"
default n
help
Some drivers can be compiled on a different platform than they are
intended to be run on. Despite they cannot be loaded there (or even
when they load they cannot be used due to missing HW support),
developers still, opposing to distributors, might want to build such
drivers to compile-test them.
If you are a developer and want to build everything available, say Y
here. If you are a user/distributor, say N here to exclude useless
drivers to be distributed.
config LOCALVERSION
string "Local version - append to kernel release"
help
Append an extra string to the end of your kernel version.
This will show up when you type uname, for example.
The string you set here will be appended after the contents of
any files with a filename matching localversion* in your
object and source tree, in that order. Your total string can
be a maximum of 64 characters.
config LOCALVERSION_AUTO
bool "Automatically append version information to the version string"
default y
help
This will try to automatically determine if the current tree is a
release tree by looking for git tags that belong to the current
top of tree revision.
A string of the format -gxxxxxxxx will be added to the localversion
if a git-based tree is found. The string generated by this will be
appended after any matching localversion* files, and after the value
set in CONFIG_LOCALVERSION.
(The actual string used here is the first eight characters produced
by running the command:
$ git rev-parse --verify HEAD
which is done within the script "scripts/setlocalversion".)
config HAVE_KERNEL_GZIP
bool
config HAVE_KERNEL_BZIP2
bool
config HAVE_KERNEL_LZMA
bool
config HAVE_KERNEL_XZ
bool
config HAVE_KERNEL_LZO
bool
config HAVE_KERNEL_LZ4
bool
choice
prompt "Kernel compression mode"
default KERNEL_GZIP
depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4
help
The linux kernel is a kind of self-extracting executable.
Several compression algorithms are available, which differ
in efficiency, compression and decompression speed.
Compression speed is only relevant when building a kernel.
Decompression speed is relevant at each boot.
If you have any problems with bzip2 or lzma compressed
kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
version of this functionality (bzip2 only), for 2.4, was
supplied by Christian Ludwig)
High compression options are mostly useful for users, who
are low on disk space (embedded systems), but for whom ram
size matters less.
If in doubt, select 'gzip'
config KERNEL_GZIP
bool "Gzip"
depends on HAVE_KERNEL_GZIP
help
The old and tried gzip compression. It provides a good balance
between compression ratio and decompression speed.
config KERNEL_BZIP2
bool "Bzip2"
depends on HAVE_KERNEL_BZIP2
help
Its compression ratio and speed is intermediate.
Decompression speed is slowest among the choices. The kernel
size is about 10% smaller with bzip2, in comparison to gzip.
Bzip2 uses a large amount of memory. For modern kernels you
will need at least 8MB RAM or more for booting.
config KERNEL_LZMA
bool "LZMA"
depends on HAVE_KERNEL_LZMA
help
This compression algorithm's ratio is best. Decompression speed
is between gzip and bzip2. Compression is slowest.
The kernel size is about 33% smaller with LZMA in comparison to gzip.
config KERNEL_XZ
bool "XZ"
depends on HAVE_KERNEL_XZ
help
XZ uses the LZMA2 algorithm and instruction set specific
BCJ filters which can improve compression ratio of executable
code. The size of the kernel is about 30% smaller with XZ in
comparison to gzip. On architectures for which there is a BCJ
filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
will create a few percent smaller kernel than plain LZMA.
The speed is about the same as with LZMA: The decompression
speed of XZ is better than that of bzip2 but worse than gzip
and LZO. Compression is slow.
config KERNEL_LZO
bool "LZO"
depends on HAVE_KERNEL_LZO
help
Its compression ratio is the poorest among the choices. The kernel
size is about 10% bigger than gzip; however its speed
(both compression and decompression) is the fastest.
config KERNEL_LZ4
bool "LZ4"
depends on HAVE_KERNEL_LZ4
help
LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
A preliminary version of LZ4 de/compression tool is available at
<https://code.google.com/p/lz4/>.
Its compression ratio is worse than LZO. The size of the kernel
is about 8% bigger than LZO. But the decompression speed is
faster than LZO.
endchoice
config DEFAULT_HOSTNAME
string "Default hostname"
default "(none)"
help
This option determines the default system hostname before userspace
calls sethostname(2). The kernel traditionally uses "(none)" here,
but you may wish to use a different default here to make a minimal
system more usable with less configuration.
config SWAP
bool "Support for paging of anonymous memory (swap)"
depends on MMU && BLOCK
default y
help
This option allows you to choose whether you want to have support
for so called swap devices or swap files in your kernel that are
used to provide more virtual memory than the actual RAM present
in your computer. If unsure say Y.
config SYSVIPC
bool "System V IPC"
---help---
Inter Process Communication is a suite of library functions and
system calls which let processes (running programs) synchronize and
exchange information. It is generally considered to be a good thing,
and some programs won't run unless you say Y here. In particular, if
you want to run the DOS emulator dosemu under Linux (read the
DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
you'll need to say Y here.
You can find documentation about IPC with "info ipc" and also in
section 6.4 of the Linux Programmer's Guide, available from
<http://www.tldp.org/guides.html>.
config SYSVIPC_SYSCTL
bool
depends on SYSVIPC
depends on SYSCTL
default y
config POSIX_MQUEUE
bool "POSIX Message Queues"
depends on NET
---help---
POSIX variant of message queues is a part of IPC. In POSIX message
queues every message has a priority which decides about succession
of receiving it by a process. If you want to compile and run
programs written e.g. for Solaris with use of its POSIX message
queues (functions mq_*) say Y here.
POSIX message queues are visible as a filesystem called 'mqueue'
and can be mounted somewhere if you want to do filesystem
operations on message queues.
If unsure, say Y.
config POSIX_MQUEUE_SYSCTL
bool
depends on POSIX_MQUEUE
depends on SYSCTL
default y
config CROSS_MEMORY_ATTACH
bool "Enable process_vm_readv/writev syscalls"
depends on MMU
default y
help
Enabling this option adds the system calls process_vm_readv and
process_vm_writev which allow a process with the correct privileges
to directly read from or write to another process' address space.
See the man page for more details.
config FHANDLE
bool "open by fhandle syscalls"
select EXPORTFS
help
If you say Y here, a user level program will be able to map
file names to handle and then later use the handle for
different file system operations. This is useful in implementing
userspace file servers, which now track files using handles instead
of names. The handle would remain the same even if file names
get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
syscalls.
config USELIB
bool "uselib syscall"
default y
help
This option enables the uselib syscall, a system call used in the
dynamic linker from libc5 and earlier. glibc does not use this
system call. If you intend to run programs built on libc5 or
earlier, you may need to enable this syscall. Current systems
running glibc can safely disable this.
config AUDIT
bool "Auditing support"
depends on NET
help
Enable auditing infrastructure that can be used with another
kernel subsystem, such as SELinux (which requires this for
logging of avc messages output). Does not do system-call
auditing without CONFIG_AUDITSYSCALL.
config HAVE_ARCH_AUDITSYSCALL
bool
config AUDITSYSCALL
bool "Enable system-call auditing support"
depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
default y if SECURITY_SELINUX
help
Enable low-overhead system-call auditing infrastructure that
can be used independently or with another kernel subsystem,
such as SELinux.
config AUDIT_WATCH
def_bool y
depends on AUDITSYSCALL
select FSNOTIFY
config AUDIT_TREE
def_bool y
depends on AUDITSYSCALL
select FSNOTIFY
source "kernel/irq/Kconfig"
source "kernel/time/Kconfig"
menu "CPU/Task time and stats accounting"
config VIRT_CPU_ACCOUNTING
bool
choice
prompt "Cputime accounting"
default TICK_CPU_ACCOUNTING if !PPC64
default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
# Kind of a stub config for the pure tick based cputime accounting
config TICK_CPU_ACCOUNTING
bool "Simple tick based cputime accounting"
depends on !S390 && !NO_HZ_FULL
help
This is the basic tick based cputime accounting that maintains
statistics about user, system and idle time spent on per jiffies
granularity.
If unsure, say Y.
config VIRT_CPU_ACCOUNTING_NATIVE
bool "Deterministic task and CPU time accounting"
depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
select VIRT_CPU_ACCOUNTING
help
Select this option to enable more accurate task and CPU time
accounting. This is done by reading a CPU counter on each
kernel entry and exit and on transitions within the kernel
between system, softirq and hardirq state, so there is a
small performance impact. In the case of s390 or IBM POWER > 5,
this also enables accounting of stolen time on logically-partitioned
systems.
config VIRT_CPU_ACCOUNTING_GEN
bool "Full dynticks CPU time accounting"
depends on HAVE_CONTEXT_TRACKING
depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
select VIRT_CPU_ACCOUNTING
select CONTEXT_TRACKING
help
Select this option to enable task and CPU time accounting on full
dynticks systems. This accounting is implemented by watching every
kernel-user boundaries using the context tracking subsystem.
The accounting is thus performed at the expense of some significant
overhead.
For now this is only useful if you are working on the full
dynticks subsystem development.
If unsure, say N.
config IRQ_TIME_ACCOUNTING
bool "Fine granularity task level IRQ time accounting"
depends on HAVE_IRQ_TIME_ACCOUNTING && !NO_HZ_FULL
help
Select this option to enable fine granularity task irq time
accounting. This is done by reading a timestamp on each
transitions between softirq and hardirq state, so there can be a
small performance impact.
If in doubt, say N here.
endchoice
config BSD_PROCESS_ACCT
bool "BSD Process Accounting"
depends on MULTIUSER
help
If you say Y here, a user level program will be able to instruct the
kernel (via a special system call) to write process accounting
information to a file: whenever a process exits, information about
that process will be appended to the file by the kernel. The
information includes things such as creation time, owning user,
command name, memory usage, controlling terminal etc. (the complete
list is in the struct acct in <file:include/linux/acct.h>). It is
up to the user level program to do useful things with this
information. This is generally a good idea, so say Y.
config BSD_PROCESS_ACCT_V3
bool "BSD Process Accounting version 3 file format"
depends on BSD_PROCESS_ACCT
default n
help
If you say Y here, the process accounting information is written
in a new file format that also logs the process IDs of each
process and it's parent. Note that this file format is incompatible
with previous v0/v1/v2 file formats, so you will need updated tools
for processing it. A preliminary version of these tools is available
at <http://www.gnu.org/software/acct/>.
config TASKSTATS
bool "Export task/process statistics through netlink"
depends on NET
depends on MULTIUSER
default n
help
Export selected statistics for tasks/processes through the
generic netlink interface. Unlike BSD process accounting, the
statistics are available during the lifetime of tasks/processes as
responses to commands. Like BSD accounting, they are sent to user
space on task exit.
Say N if unsure.
config TASK_DELAY_ACCT
bool "Enable per-task delay accounting"
depends on TASKSTATS
select SCHED_INFO
help
Collect information on time spent by a task waiting for system
resources like cpu, synchronous block I/O completion and swapping
in pages. Such statistics can help in setting a task's priorities
relative to other tasks for cpu, io, rss limits etc.
Say N if unsure.
config TASK_XACCT
bool "Enable extended accounting over taskstats"
depends on TASKSTATS
help
Collect extended task accounting data and send the data
to userland for processing over the taskstats interface.
Say N if unsure.
config TASK_IO_ACCOUNTING
bool "Enable per-task storage I/O accounting"
depends on TASK_XACCT
help
Collect information on the number of bytes of storage I/O which this
task has caused.
Say N if unsure.
endmenu # "CPU/Task time and stats accounting"
menu "RCU Subsystem"
config TREE_RCU
bool
default y if !PREEMPT && SMP
help
This option selects the RCU implementation that is
designed for very large SMP system with hundreds or
thousands of CPUs. It also scales down nicely to
smaller systems.
config PREEMPT_RCU
bool
default y if PREEMPT
help
This option selects the RCU implementation that is
designed for very large SMP systems with hundreds or
thousands of CPUs, but for which real-time response
is also required. It also scales down nicely to
smaller systems.
Select this option if you are unsure.
config TINY_RCU
bool
default y if !PREEMPT && !SMP
help
This option selects the RCU implementation that is
designed for UP systems from which real-time response
is not required. This option greatly reduces the
memory footprint of RCU.
config RCU_EXPERT
bool "Make expert-level adjustments to RCU configuration"
default n
help
This option needs to be enabled if you wish to make
expert-level adjustments to RCU configuration. By default,
no such adjustments can be made, which has the often-beneficial
side-effect of preventing "make oldconfig" from asking you all
sorts of detailed questions about how you would like numerous
obscure RCU options to be set up.
Say Y if you need to make expert-level adjustments to RCU.
Say N if you are unsure.
config SRCU
bool
help
This option selects the sleepable version of RCU. This version
permits arbitrary sleeping or blocking within RCU read-side critical
sections.
config TASKS_RCU
bool
default n
select SRCU
help
This option enables a task-based RCU implementation that uses
only voluntary context switch (not preemption!), idle, and
user-mode execution as quiescent states.
config RCU_STALL_COMMON
def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE )
help
This option enables RCU CPU stall code that is common between
the TINY and TREE variants of RCU. The purpose is to allow
the tiny variants to disable RCU CPU stall warnings, while
making these warnings mandatory for the tree variants.
config CONTEXT_TRACKING
bool
config CONTEXT_TRACKING_FORCE
bool "Force context tracking"
depends on CONTEXT_TRACKING
default y if !NO_HZ_FULL
help
The major pre-requirement for full dynticks to work is to
support the context tracking subsystem. But there are also
other dependencies to provide in order to make the full
dynticks working.
This option stands for testing when an arch implements the
context tracking backend but doesn't yet fullfill all the
requirements to make the full dynticks feature working.
Without the full dynticks, there is no way to test the support
for context tracking and the subsystems that rely on it: RCU
userspace extended quiescent state and tickless cputime
accounting. This option copes with the absence of the full
dynticks subsystem by forcing the context tracking on all
CPUs in the system.
Say Y only if you're working on the development of an
architecture backend for the context tracking.
Say N otherwise, this option brings an overhead that you
don't want in production.
config RCU_FANOUT
int "Tree-based hierarchical RCU fanout value"
range 2 64 if 64BIT
range 2 32 if !64BIT
depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
default 64 if 64BIT
default 32 if !64BIT
help
This option controls the fanout of hierarchical implementations
of RCU, allowing RCU to work efficiently on machines with
large numbers of CPUs. This value must be at least the fourth
root of NR_CPUS, which allows NR_CPUS to be insanely large.
The default value of RCU_FANOUT should be used for production
systems, but if you are stress-testing the RCU implementation
itself, small RCU_FANOUT values allow you to test large-system
code paths on small(er) systems.
Select a specific number if testing RCU itself.
Take the default if unsure.
config RCU_FANOUT_LEAF
int "Tree-based hierarchical RCU leaf-level fanout value"
range 2 64 if 64BIT
range 2 32 if !64BIT
depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
default 16
help
This option controls the leaf-level fanout of hierarchical
implementations of RCU, and allows trading off cache misses
against lock contention. Systems that synchronize their
scheduling-clock interrupts for energy-efficiency reasons will
want the default because the smaller leaf-level fanout keeps
lock contention levels acceptably low. Very large systems
(hundreds or thousands of CPUs) will instead want to set this
value to the maximum value possible in order to reduce the
number of cache misses incurred during RCU's grace-period
initialization. These systems tend to run CPU-bound, and thus
are not helped by synchronized interrupts, and thus tend to
skew them, which reduces lock contention enough that large
leaf-level fanouts work well.
Select a specific number if testing RCU itself.
Select the maximum permissible value for large systems.
Take the default if unsure.
config RCU_FAST_NO_HZ
bool "Accelerate last non-dyntick-idle CPU's grace periods"
depends on NO_HZ_COMMON && SMP && RCU_EXPERT
default n
help
This option permits CPUs to enter dynticks-idle state even if
they have RCU callbacks queued, and prevents RCU from waking
these CPUs up more than roughly once every four jiffies (by
default, you can adjust this using the rcutree.rcu_idle_gp_delay
parameter), thus improving energy efficiency. On the other
hand, this option increases the duration of RCU grace periods,
for example, slowing down synchronize_rcu().
Say Y if energy efficiency is critically important, and you
don't care about increased grace-period durations.
Say N if you are unsure.
config TREE_RCU_TRACE
def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU )
select DEBUG_FS
help
This option provides tracing for the TREE_RCU and
PREEMPT_RCU implementations, permitting Makefile to
trivially select kernel/rcutree_trace.c.
config RCU_BOOST
bool "Enable RCU priority boosting"
depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT
default n
help
This option boosts the priority of preempted RCU readers that
block the current preemptible RCU grace period for too long.
This option also prevents heavy loads from blocking RCU
callback invocation for all flavors of RCU.
Say Y here if you are working with real-time apps or heavy loads
Say N here if you are unsure.
config RCU_KTHREAD_PRIO
int "Real-time priority to use for RCU worker threads"
range 1 99 if RCU_BOOST
range 0 99 if !RCU_BOOST
default 1 if RCU_BOOST
default 0 if !RCU_BOOST
depends on RCU_EXPERT
help
This option specifies the SCHED_FIFO priority value that will be
assigned to the rcuc/n and rcub/n threads and is also the value
used for RCU_BOOST (if enabled). If you are working with a
real-time application that has one or more CPU-bound threads
running at a real-time priority level, you should set
RCU_KTHREAD_PRIO to a priority higher than the highest-priority
real-time CPU-bound application thread. The default RCU_KTHREAD_PRIO
value of 1 is appropriate in the common case, which is real-time
applications that do not have any CPU-bound threads.
Some real-time applications might not have a single real-time
thread that saturates a given CPU, but instead might have
multiple real-time threads that, taken together, fully utilize
that CPU. In this case, you should set RCU_KTHREAD_PRIO to
a priority higher than the lowest-priority thread that is
conspiring to prevent the CPU from running any non-real-time
tasks. For example, if one thread at priority 10 and another
thread at priority 5 are between themselves fully consuming
the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be
set to priority 6 or higher.
Specify the real-time priority, or take the default if unsure.
config RCU_BOOST_DELAY
int "Milliseconds to delay boosting after RCU grace-period start"
range 0 3000
depends on RCU_BOOST
default 500
help
This option specifies the time to wait after the beginning of
a given grace period before priority-boosting preempted RCU
readers blocking that grace period. Note that any RCU reader
blocking an expedited RCU grace period is boosted immediately.
Accept the default if unsure.
config RCU_NOCB_CPU
bool "Offload RCU callback processing from boot-selected CPUs"
depends on TREE_RCU || PREEMPT_RCU
depends on RCU_EXPERT || NO_HZ_FULL
default n
help
Use this option to reduce OS jitter for aggressive HPC or
real-time workloads. It can also be used to offload RCU
callback invocation to energy-efficient CPUs in battery-powered
asymmetric multiprocessors.
This option offloads callback invocation from the set of
CPUs specified at boot time by the rcu_nocbs parameter.
For each such CPU, a kthread ("rcuox/N") will be created to
invoke callbacks, where the "N" is the CPU being offloaded,
and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and
"s" for RCU-sched. Nothing prevents this kthread from running
on the specified CPUs, but (1) the kthreads may be preempted
between each callback, and (2) affinity or cgroups can be used
to force the kthreads to run on whatever set of CPUs is desired.
Say Y here if you want to help to debug reduced OS jitter.
Say N here if you are unsure.
choice
prompt "Build-forced no-CBs CPUs"
default RCU_NOCB_CPU_NONE
depends on RCU_NOCB_CPU
help
This option allows no-CBs CPUs (whose RCU callbacks are invoked
from kthreads rather than from softirq context) to be specified
at build time. Additional no-CBs CPUs may be specified by
the rcu_nocbs= boot parameter.
config RCU_NOCB_CPU_NONE
bool "No build_forced no-CBs CPUs"
help
This option does not force any of the CPUs to be no-CBs CPUs.
Only CPUs designated by the rcu_nocbs= boot parameter will be
no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
kthreads whose names begin with "rcuo". All other CPUs will
invoke their own RCU callbacks in softirq context.
Select this option if you want to choose no-CBs CPUs at
boot time, for example, to allow testing of different no-CBs
configurations without having to rebuild the kernel each time.
config RCU_NOCB_CPU_ZERO
bool "CPU 0 is a build_forced no-CBs CPU"
help
This option forces CPU 0 to be a no-CBs CPU, so that its RCU
callbacks are invoked by a per-CPU kthread whose name begins
with "rcuo". Additional CPUs may be designated as no-CBs
CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
All other CPUs will invoke their own RCU callbacks in softirq
context.
Select this if CPU 0 needs to be a no-CBs CPU for real-time
or energy-efficiency reasons, but the real reason it exists
is to ensure that randconfig testing covers mixed systems.
config RCU_NOCB_CPU_ALL
bool "All CPUs are build_forced no-CBs CPUs"
help
This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs=
boot parameter will be ignored. All CPUs' RCU callbacks will
be executed in the context of per-CPU rcuo kthreads created for
this purpose. Assuming that the kthreads whose names start with
"rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
on the remaining CPUs, but might decrease memory locality during
RCU-callback invocation, thus potentially degrading throughput.
Select this if all CPUs need to be no-CBs CPUs for real-time
or energy-efficiency reasons.
endchoice
config RCU_EXPEDITE_BOOT
bool
default n
help
This option enables expedited grace periods at boot time,
as if rcu_expedite_gp() had been invoked early in boot.
The corresponding rcu_unexpedite_gp() is invoked from
rcu_end_inkernel_boot(), which is intended to be invoked
at the end of the kernel-only boot sequence, just before
init is exec'ed.
Accept the default if unsure.
endmenu # "RCU Subsystem"
config BUILD_BIN2C
bool
default n
config IKCONFIG
tristate "Kernel .config support"
select BUILD_BIN2C
---help---
This option enables the complete Linux kernel ".config" file
contents to be saved in the kernel. It provides documentation
of which kernel options are used in a running kernel or in an
on-disk kernel. This information can be extracted from the kernel
image file with the script scripts/extract-ikconfig and used as
input to rebuild the current kernel or to build another kernel.
It can also be extracted from a running kernel by reading
/proc/config.gz if enabled (below).
config IKCONFIG_PROC
bool "Enable access to .config through /proc/config.gz"
depends on IKCONFIG && PROC_FS
---help---
This option enables access to the kernel configuration file
through /proc/config.gz.
config LOG_BUF_SHIFT
int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
range 12 25
default 17
depends on PRINTK
help
Select the minimal kernel log buffer size as a power of 2.
The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
parameter, see below. Any higher size also might be forced
by "log_buf_len" boot parameter.
Examples:
17 => 128 KB
16 => 64 KB
15 => 32 KB
14 => 16 KB
13 => 8 KB
12 => 4 KB
config LOG_CPU_MAX_BUF_SHIFT
int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
depends on SMP
range 0 21
default 12 if !BASE_SMALL
default 0 if BASE_SMALL
depends on PRINTK
help
This option allows to increase the default ring buffer size
according to the number of CPUs. The value defines the contribution
of each CPU as a power of 2. The used space is typically only few
lines however it might be much more when problems are reported,
e.g. backtraces.
The increased size means that a new buffer has to be allocated and
the original static one is unused. It makes sense only on systems
with more CPUs. Therefore this value is used only when the sum of
contributions is greater than the half of the default kernel ring
buffer as defined by LOG_BUF_SHIFT. The default values are set
so that more than 64 CPUs are needed to trigger the allocation.
Also this option is ignored when "log_buf_len" kernel parameter is
used as it forces an exact (power of two) size of the ring buffer.
The number of possible CPUs is used for this computation ignoring
hotplugging making the compuation optimal for the the worst case
scenerio while allowing a simple algorithm to be used from bootup.
Examples shift values and their meaning:
17 => 128 KB for each CPU
16 => 64 KB for each CPU
15 => 32 KB for each CPU
14 => 16 KB for each CPU
13 => 8 KB for each CPU
12 => 4 KB for each CPU
#
# Architectures with an unreliable sched_clock() should select this:
#
config HAVE_UNSTABLE_SCHED_CLOCK
bool
config GENERIC_SCHED_CLOCK
bool
#
# For architectures that want to enable the support for NUMA-affine scheduler
# balancing logic:
#
config ARCH_SUPPORTS_NUMA_BALANCING
bool
#
# For architectures that prefer to flush all TLBs after a number of pages
# are unmapped instead of sending one IPI per page to flush. The architecture
# must provide guarantees on what happens if a clean TLB cache entry is
# written after the unmap. Details are in mm/rmap.c near the check for
# should_defer_flush. The architecture should also consider if the full flush
# and the refill costs are offset by the savings of sending fewer IPIs.
config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
bool
#
# For architectures that know their GCC __int128 support is sound
#
config ARCH_SUPPORTS_INT128
bool
# For architectures that (ab)use NUMA to represent different memory regions
# all cpu-local but of different latencies, such as SuperH.
#
config ARCH_WANT_NUMA_VARIABLE_LOCALITY
bool
config NUMA_BALANCING
bool "Memory placement aware NUMA scheduler"
depends on ARCH_SUPPORTS_NUMA_BALANCING
depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
depends on SMP && NUMA && MIGRATION
help
This option adds support for automatic NUMA aware memory/task placement.
The mechanism is quite primitive and is based on migrating memory when
it has references to the node the task is running on.
This system will be inactive on UMA systems.
config NUMA_BALANCING_DEFAULT_ENABLED
bool "Automatically enable NUMA aware memory/task placement"
default y
depends on NUMA_BALANCING
help
If set, automatic NUMA balancing will be enabled if running on a NUMA
machine.
menuconfig CGROUPS
bool "Control Group support"
select KERNFS
help
This option adds support for grouping sets of processes together, for
use with process control subsystems such as Cpusets, CFS, memory
controls or device isolation.
See
- Documentation/scheduler/sched-design-CFS.txt (CFS)
- Documentation/cgroups/ (features for grouping, isolation
and resource control)
Say N if unsure.
if CGROUPS
config CGROUP_DEBUG
bool "Example debug cgroup subsystem"
default n
help
This option enables a simple cgroup subsystem that
exports useful debugging information about the cgroups
framework.
Say N if unsure.
config CGROUP_FREEZER
bool "Freezer cgroup subsystem"
help
Provides a way to freeze and unfreeze all tasks in a
cgroup.
config CGROUP_PIDS
bool "PIDs cgroup subsystem"
help
Provides enforcement of process number limits in the scope of a
cgroup. Any attempt to fork more processes than is allowed in the
cgroup will fail. PIDs are fundamentally a global resource because it
is fairly trivial to reach PID exhaustion before you reach even a
conservative kmemcg limit. As a result, it is possible to grind a
system to halt without being limited by other cgroup policies. The
PIDs cgroup subsystem is designed to stop this from happening.
It should be noted that organisational operations (such as attaching
to a cgroup hierarchy will *not* be blocked by the PIDs subsystem),
since the PIDs limit only affects a process's ability to fork, not to
attach to a cgroup.
config CGROUP_DEVICE
bool "Device controller for cgroups"
help
Provides a cgroup implementing whitelists for devices which
a process in the cgroup can mknod or open.
config CPUSETS
bool "Cpuset support"
help
This option will let you create and manage CPUSETs which
allow dynamically partitioning a system into sets of CPUs and
Memory Nodes and assigning tasks to run only within those sets.
This is primarily useful on large SMP or NUMA systems.
Say N if unsure.
config PROC_PID_CPUSET
bool "Include legacy /proc/<pid>/cpuset file"
depends on CPUSETS
default y
config CGROUP_CPUACCT
bool "Simple CPU accounting cgroup subsystem"
help
Provides a simple Resource Controller for monitoring the
total CPU consumed by the tasks in a cgroup.
config PAGE_COUNTER
bool
config MEMCG
bool "Memory Resource Controller for Control Groups"
select PAGE_COUNTER
select EVENTFD
help
Provides a memory resource controller that manages both anonymous
memory and page cache. (See Documentation/cgroups/memory.txt)
config MEMCG_SWAP
bool "Memory Resource Controller Swap Extension"
depends on MEMCG && SWAP
help
Add swap management feature to memory resource controller. When you
enable this, you can limit mem+swap usage per cgroup. In other words,
when you disable this, memory resource controller has no cares to
usage of swap...a process can exhaust all of the swap. This extension
is useful when you want to avoid exhaustion swap but this itself
adds more overheads and consumes memory for remembering information.
Especially if you use 32bit system or small memory system, please
be careful about enabling this. When memory resource controller
is disabled by boot option, this will be automatically disabled and
there will be no overhead from this. Even when you set this config=y,
if boot option "swapaccount=0" is set, swap will not be accounted.
Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
size is 4096bytes, 512k per 1Gbytes of swap.
config MEMCG_SWAP_ENABLED
bool "Memory Resource Controller Swap Extension enabled by default"
depends on MEMCG_SWAP
default y
help
Memory Resource Controller Swap Extension comes with its price in
a bigger memory consumption. General purpose distribution kernels
which want to enable the feature but keep it disabled by default
and let the user enable it by swapaccount=1 boot command line
parameter should have this option unselected.
For those who want to have the feature enabled by default should
select this option (if, for some reason, they need to disable it
then swapaccount=0 does the trick).
config MEMCG_KMEM
bool "Memory Resource Controller Kernel Memory accounting"
depends on MEMCG
depends on SLUB || SLAB
help
The Kernel Memory extension for Memory Resource Controller can limit
the amount of memory used by kernel objects in the system. Those are
fundamentally different from the entities handled by the standard
Memory Controller, which are page-based, and can be swapped. Users of
the kmem extension can use it to guarantee that no group of processes
will ever exhaust kernel resources alone.
config CGROUP_HUGETLB
bool "HugeTLB Resource Controller for Control Groups"
depends on HUGETLB_PAGE
select PAGE_COUNTER
default n
help
Provides a cgroup Resource Controller for HugeTLB pages.
When you enable this, you can put a per cgroup limit on HugeTLB usage.
The limit is enforced during page fault. Since HugeTLB doesn't
support page reclaim, enforcing the limit at page fault time implies
that, the application will get SIGBUS signal if it tries to access
HugeTLB pages beyond its limit. This requires the application to know
beforehand how much HugeTLB pages it would require for its use. The
control group is tracked in the third page lru pointer. This means
that we cannot use the controller with huge page less than 3 pages.
config CGROUP_PERF
bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
depends on PERF_EVENTS && CGROUPS
help
This option extends the per-cpu mode to restrict monitoring to
threads which belong to the cgroup specified and run on the
designated cpu.
Say N if unsure.
menuconfig CGROUP_SCHED
bool "Group CPU scheduler"
default n
help
This feature lets CPU scheduler recognize task groups and control CPU
bandwidth allocation to such task groups. It uses cgroups to group
tasks.
if CGROUP_SCHED
config FAIR_GROUP_SCHED
bool "Group scheduling for SCHED_OTHER"
depends on CGROUP_SCHED
default CGROUP_SCHED
config CFS_BANDWIDTH
bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
depends on FAIR_GROUP_SCHED
default n
help
This option allows users to define CPU bandwidth rates (limits) for
tasks running within the fair group scheduler. Groups with no limit
set are considered to be unconstrained and will run with no
restriction.
See tip/Documentation/scheduler/sched-bwc.txt for more information.
config RT_GROUP_SCHED
bool "Group scheduling for SCHED_RR/FIFO"
depends on CGROUP_SCHED
default n
help
This feature lets you explicitly allocate real CPU bandwidth
to task groups. If enabled, it will also make it impossible to
schedule realtime tasks for non-root users until you allocate
realtime bandwidth for them.
See Documentation/scheduler/sched-rt-group.txt for more information.
endif #CGROUP_SCHED
config BLK_CGROUP
bool "Block IO controller"
depends on BLOCK
default n
---help---
Generic block IO controller cgroup interface. This is the common
cgroup interface which should be used by various IO controlling
policies.
Currently, CFQ IO scheduler uses it to recognize task groups and
control disk bandwidth allocation (proportional time slice allocation)
to such task groups. It is also used by bio throttling logic in
block layer to implement upper limit in IO rates on a device.
This option only enables generic Block IO controller infrastructure.
One needs to also enable actual IO controlling logic/policy. For
enabling proportional weight division of disk bandwidth in CFQ, set
CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
CONFIG_BLK_DEV_THROTTLING=y.
See Documentation/cgroups/blkio-controller.txt for more information.
config DEBUG_BLK_CGROUP
bool "Enable Block IO controller debugging"
depends on BLK_CGROUP
default n
---help---
Enable some debugging help. Currently it exports additional stat
files in a cgroup which can be useful for debugging.
config CGROUP_WRITEBACK
bool
depends on MEMCG && BLK_CGROUP
default y
endif # CGROUPS
config CHECKPOINT_RESTORE
bool "Checkpoint/restore support" if EXPERT
select PROC_CHILDREN
default n
help
Enables additional kernel features in a sake of checkpoint/restore.
In particular it adds auxiliary prctl codes to setup process text,
data and heap segment sizes, and a few additional /proc filesystem
entries.
If unsure, say N here.
menuconfig NAMESPACES
bool "Namespaces support" if EXPERT
depends on MULTIUSER
default !EXPERT
help
Provides the way to make tasks work with different objects using
the same id. For example same IPC id may refer to different objects
or same user id or pid may refer to different tasks when used in
different namespaces.
if NAMESPACES
config UTS_NS
bool "UTS namespace"
default y
help
In this namespace tasks see different info provided with the
uname() system call
config IPC_NS
bool "IPC namespace"
depends on (SYSVIPC || POSIX_MQUEUE)
default y
help
In this namespace tasks work with IPC ids which correspond to
different IPC objects in different namespaces.
config USER_NS
bool "User namespace"
default n
help
This allows containers, i.e. vservers, to use user namespaces
to provide different user info for different servers.
When user namespaces are enabled in the kernel it is
recommended that the MEMCG and MEMCG_KMEM options also be
enabled and that user-space use the memory control groups to
limit the amount of memory a memory unprivileged users can
use.
If unsure, say N.
config PID_NS
bool "PID Namespaces"
default y
help
Support process id namespaces. This allows having multiple
processes with the same pid as long as they are in different
pid namespaces. This is a building block of containers.
config NET_NS
bool "Network namespace"
depends on NET
default y
help
Allow user space to create what appear to be multiple instances
of the network stack.
endif # NAMESPACES
config SCHED_AUTOGROUP
bool "Automatic process group scheduling"
select CGROUPS
select CGROUP_SCHED
select FAIR_GROUP_SCHED
help
This option optimizes the scheduler for common desktop workloads by
automatically creating and populating task groups. This separation
of workloads isolates aggressive CPU burners (like build jobs) from
desktop applications. Task group autogeneration is currently based
upon task session.
config SYSFS_DEPRECATED
bool "Enable deprecated sysfs features to support old userspace tools"
depends on SYSFS
default n
help
This option adds code that switches the layout of the "block" class
devices, to not show up in /sys/class/block/, but only in
/sys/block/.
This switch is only active when the sysfs.deprecated=1 boot option is
passed or the SYSFS_DEPRECATED_V2 option is set.
This option allows new kernels to run on old distributions and tools,
which might get confused by /sys/class/block/. Since 2007/2008 all
major distributions and tools handle this just fine.
Recent distributions and userspace tools after 2009/2010 depend on
the existence of /sys/class/block/, and will not work with this
option enabled.
Only if you are using a new kernel on an old distribution, you might
need to say Y here.
config SYSFS_DEPRECATED_V2
bool "Enable deprecated sysfs features by default"
default n
depends on SYSFS
depends on SYSFS_DEPRECATED
help
Enable deprecated sysfs by default.
See the CONFIG_SYSFS_DEPRECATED option for more details about this
option.
Only if you are using a new kernel on an old distribution, you might
need to say Y here. Even then, odds are you would not need it
enabled, you can always pass the boot option if absolutely necessary.
config RELAY
bool "Kernel->user space relay support (formerly relayfs)"
help
This option enables support for relay interface support in
certain file systems (such as debugfs).
It is designed to provide an efficient mechanism for tools and
facilities to relay large amounts of data from kernel space to
user space.
If unsure, say N.
config BLK_DEV_INITRD
bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
depends on BROKEN || !FRV
help
The initial RAM filesystem is a ramfs which is loaded by the
boot loader (loadlin or lilo) and that is mounted as root
before the normal boot procedure. It is typically used to
load modules needed to mount the "real" root file system,
etc. See <file:Documentation/initrd.txt> for details.
If RAM disk support (BLK_DEV_RAM) is also included, this
also enables initial RAM disk (initrd) support and adds
15 Kbytes (more on some other architectures) to the kernel size.
If unsure say Y.
if BLK_DEV_INITRD
source "usr/Kconfig"
endif
config CC_OPTIMIZE_FOR_SIZE
bool "Optimize for size"
help
Enabling this option will pass "-Os" instead of "-O2" to
your compiler resulting in a smaller kernel.
If unsure, say N.
config SYSCTL
bool
config ANON_INODES
bool
config HAVE_UID16
bool
config SYSCTL_EXCEPTION_TRACE
bool
help
Enable support for /proc/sys/debug/exception-trace.
config SYSCTL_ARCH_UNALIGN_NO_WARN
bool
help
Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
Allows arch to define/use @no_unaligned_warning to possibly warn
about unaligned access emulation going on under the hood.
config SYSCTL_ARCH_UNALIGN_ALLOW
bool
help
Enable support for /proc/sys/kernel/unaligned-trap
Allows arches to define/use @unaligned_enabled to runtime toggle
the unaligned access emulation.
see arch/parisc/kernel/unaligned.c for reference
config HAVE_PCSPKR_PLATFORM
bool
# interpreter that classic socket filters depend on
config BPF
bool
menuconfig EXPERT
bool "Configure standard kernel features (expert users)"
# Unhide debug options, to make the on-by-default options visible
select DEBUG_KERNEL
help
This option allows certain base kernel options and settings
to be disabled or tweaked. This is for specialized
environments which can tolerate a "non-standard" kernel.
Only use this if you really know what you are doing.
config UID16
bool "Enable 16-bit UID system calls" if EXPERT
depends on HAVE_UID16 && MULTIUSER
default y
help
This enables the legacy 16-bit UID syscall wrappers.
config MULTIUSER
bool "Multiple users, groups and capabilities support" if EXPERT
default y
help
This option enables support for non-root users, groups and
capabilities.
If you say N here, all processes will run with UID 0, GID 0, and all
possible capabilities. Saying N here also compiles out support for
system calls related to UIDs, GIDs, and capabilities, such as setuid,
setgid, and capset.
If unsure, say Y here.
config SGETMASK_SYSCALL
bool "sgetmask/ssetmask syscalls support" if EXPERT
def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
---help---
sys_sgetmask and sys_ssetmask are obsolete system calls
no longer supported in libc but still enabled by default in some
architectures.
If unsure, leave the default option here.
config SYSFS_SYSCALL
bool "Sysfs syscall support" if EXPERT
default y
---help---
sys_sysfs is an obsolete system call no longer supported in libc.
Note that disabling this option is more secure but might break
compatibility with some systems.
If unsure say Y here.
config SYSCTL_SYSCALL
bool "Sysctl syscall support" if EXPERT
depends on PROC_SYSCTL
default n
select SYSCTL
---help---
sys_sysctl uses binary paths that have been found challenging
to properly maintain and use. The interface in /proc/sys
using paths with ascii names is now the primary path to this
information.
Almost nothing using the binary sysctl interface so if you are
trying to save some space it is probably safe to disable this,
making your kernel marginally smaller.
If unsure say N here.
config KALLSYMS
bool "Load all symbols for debugging/ksymoops" if EXPERT
default y
help
Say Y here to let the kernel print out symbolic crash information and
symbolic stack backtraces. This increases the size of the kernel
somewhat, as all symbols have to be loaded into the kernel image.
config KALLSYMS_ALL
bool "Include all symbols in kallsyms"
depends on DEBUG_KERNEL && KALLSYMS
help
Normally kallsyms only contains the symbols of functions for nicer
OOPS messages and backtraces (i.e., symbols from the text and inittext
sections). This is sufficient for most cases. And only in very rare
cases (e.g., when a debugger is used) all symbols are required (e.g.,
names of variables from the data sections, etc).
This option makes sure that all symbols are loaded into the kernel
image (i.e., symbols from all sections) in cost of increased kernel
size (depending on the kernel configuration, it may be 300KiB or
something like this).
Say N unless you really need all symbols.
config PRINTK
default y
bool "Enable support for printk" if EXPERT
select IRQ_WORK
help
This option enables normal printk support. Removing it
eliminates most of the message strings from the kernel image
and makes the kernel more or less silent. As this makes it
very difficult to diagnose system problems, saying N here is
strongly discouraged.
config BUG
bool "BUG() support" if EXPERT
default y
help
Disabling this option eliminates support for BUG and WARN, reducing
the size of your kernel image and potentially quietly ignoring
numerous fatal conditions. You should only consider disabling this
option for embedded systems with no facilities for reporting errors.
Just say Y.
config ELF_CORE
depends on COREDUMP
default y
bool "Enable ELF core dumps" if EXPERT
help
Enable support for generating core dumps. Disabling saves about 4k.
config PCSPKR_PLATFORM
bool "Enable PC-Speaker support" if EXPERT
depends on HAVE_PCSPKR_PLATFORM
select I8253_LOCK
default y
help
This option allows to disable the internal PC-Speaker
support, saving some memory.
config BASE_FULL
default y
bool "Enable full-sized data structures for core" if EXPERT
help
Disabling this option reduces the size of miscellaneous core
kernel data structures. This saves memory on small machines,
but may reduce performance.
config FUTEX
bool "Enable futex support" if EXPERT
default y
select RT_MUTEXES
help
Disabling this option will cause the kernel to be built without
support for "fast userspace mutexes". The resulting kernel may not
run glibc-based applications correctly.
config HAVE_FUTEX_CMPXCHG
bool
depends on FUTEX
help
Architectures should select this if futex_atomic_cmpxchg_inatomic()
is implemented and always working. This removes a couple of runtime
checks.
config EPOLL
bool "Enable eventpoll support" if EXPERT
default y
select ANON_INODES
help
Disabling this option will cause the kernel to be built without
support for epoll family of system calls.
config SIGNALFD
bool "Enable signalfd() system call" if EXPERT
select ANON_INODES
default y
help
Enable the signalfd() system call that allows to receive signals
on a file descriptor.
If unsure, say Y.
config TIMERFD
bool "Enable timerfd() system call" if EXPERT
select ANON_INODES
default y
help
Enable the timerfd() system call that allows to receive timer
events on a file descriptor.
If unsure, say Y.
config EVENTFD
bool "Enable eventfd() system call" if EXPERT
select ANON_INODES
default y
help
Enable the eventfd() system call that allows to receive both
kernel notification (ie. KAIO) or userspace notifications.
If unsure, say Y.
# syscall, maps, verifier
config BPF_SYSCALL
bool "Enable bpf() system call"
select ANON_INODES
select BPF
default n
help
Enable the bpf() system call that allows to manipulate eBPF
programs and maps via file descriptors.
config SHMEM
bool "Use full shmem filesystem" if EXPERT
default y
depends on MMU
help
The shmem is an internal filesystem used to manage shared memory.
It is backed by swap and manages resource limits. It is also exported
to userspace as tmpfs if TMPFS is enabled. Disabling this
option replaces shmem and tmpfs with the much simpler ramfs code,
which may be appropriate on small systems without swap.
config AIO
bool "Enable AIO support" if EXPERT
default y
help
This option enables POSIX asynchronous I/O which may by used
by some high performance threaded applications. Disabling
this option saves about 7k.
config ADVISE_SYSCALLS
bool "Enable madvise/fadvise syscalls" if EXPERT
default y
help
This option enables the madvise and fadvise syscalls, used by
applications to advise the kernel about their future memory or file
usage, improving performance. If building an embedded system where no
applications use these syscalls, you can disable this option to save
space.
config USERFAULTFD
bool "Enable userfaultfd() system call"
select ANON_INODES
depends on MMU
help
Enable the userfaultfd() system call that allows to intercept and
handle page faults in userland.
config PCI_QUIRKS
default y
bool "Enable PCI quirk workarounds" if EXPERT
depends on PCI
help
This enables workarounds for various PCI chipset
bugs/quirks. Disable this only if your target machine is
unaffected by PCI quirks.
config MEMBARRIER
bool "Enable membarrier() system call" if EXPERT
default y
help
Enable the membarrier() system call that allows issuing memory
barriers across all running threads, which can be used to distribute
the cost of user-space memory barriers asymmetrically by transforming
pairs of memory barriers into pairs consisting of membarrier() and a
compiler barrier.
If unsure, say Y.
config EMBEDDED
bool "Embedded system"
option allnoconfig_y
select EXPERT
help
This option should be enabled if compiling the kernel for
an embedded system so certain expert options are available
for configuration.
config HAVE_PERF_EVENTS
bool
help
See tools/perf/design.txt for details.
config PERF_USE_VMALLOC
bool
help
See tools/perf/design.txt for details
menu "Kernel Performance Events And Counters"
config PERF_EVENTS
bool "Kernel performance events and counters"
default y if PROFILING
depends on HAVE_PERF_EVENTS
select ANON_INODES
select IRQ_WORK
select SRCU
help
Enable kernel support for various performance events provided
by software and hardware.
Software events are supported either built-in or via the
use of generic tracepoints.
Most modern CPUs support performance events via performance
counter registers. These registers count the number of certain
types of hw events: such as instructions executed, cachemisses
suffered, or branches mis-predicted - without slowing down the
kernel or applications. These registers can also trigger interrupts
when a threshold number of events have passed - and can thus be
used to profile the code that runs on that CPU.
The Linux Performance Event subsystem provides an abstraction of
these software and hardware event capabilities, available via a
system call and used by the "perf" utility in tools/perf/. It
provides per task and per CPU counters, and it provides event
capabilities on top of those.
Say Y if unsure.
config DEBUG_PERF_USE_VMALLOC
default n
bool "Debug: use vmalloc to back perf mmap() buffers"
depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
select PERF_USE_VMALLOC
help
Use vmalloc memory to back perf mmap() buffers.
Mostly useful for debugging the vmalloc code on platforms
that don't require it.
Say N if unsure.
endmenu
config VM_EVENT_COUNTERS
default y
bool "Enable VM event counters for /proc/vmstat" if EXPERT
help
VM event counters are needed for event counts to be shown.
This option allows the disabling of the VM event counters
on EXPERT systems. /proc/vmstat will only show page counts
if VM event counters are disabled.
config SLUB_DEBUG
default y
bool "Enable SLUB debugging support" if EXPERT
depends on SLUB && SYSFS
help
SLUB has extensive debug support features. Disabling these can
result in significant savings in code size. This also disables
SLUB sysfs support. /sys/slab will not exist and there will be
no support for cache validation etc.
config COMPAT_BRK
bool "Disable heap randomization"
default y
help
Randomizing heap placement makes heap exploits harder, but it
also breaks ancient binaries (including anything libc5 based).
This option changes the bootup default to heap randomization
disabled, and can be overridden at runtime by setting
/proc/sys/kernel/randomize_va_space to 2.
On non-ancient distros (post-2000 ones) N is usually a safe choice.
choice
prompt "Choose SLAB allocator"
default SLUB
help
This option allows to select a slab allocator.
config SLAB
bool "SLAB"
help
The regular slab allocator that is established and known to work
well in all environments. It organizes cache hot objects in
per cpu and per node queues.
config SLUB
bool "SLUB (Unqueued Allocator)"
help
SLUB is a slab allocator that minimizes cache line usage
instead of managing queues of cached objects (SLAB approach).
Per cpu caching is realized using slabs of objects instead
of queues of objects. SLUB can use memory efficiently
and has enhanced diagnostics. SLUB is the default choice for
a slab allocator.
config SLOB
depends on EXPERT
bool "SLOB (Simple Allocator)"
help
SLOB replaces the stock allocator with a drastically simpler
allocator. SLOB is generally more space efficient but
does not perform as well on large systems.
endchoice
config SLUB_CPU_PARTIAL
default y
depends on SLUB && SMP
bool "SLUB per cpu partial cache"
help
Per cpu partial caches accellerate objects allocation and freeing
that is local to a processor at the price of more indeterminism
in the latency of the free. On overflow these caches will be cleared
which requires the taking of locks that may cause latency spikes.
Typically one would choose no for a realtime system.
config MMAP_ALLOW_UNINITIALIZED
bool "Allow mmapped anonymous memory to be uninitialized"
depends on EXPERT && !MMU
default n
help
Normally, and according to the Linux spec, anonymous memory obtained
from mmap() has it's contents cleared before it is passed to
userspace. Enabling this config option allows you to request that
mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
providing a huge performance boost. If this option is not enabled,
then the flag will be ignored.
This is taken advantage of by uClibc's malloc(), and also by
ELF-FDPIC binfmt's brk and stack allocator.
Because of the obvious security issues, this option should only be
enabled on embedded devices where you control what is run in
userspace. Since that isn't generally a problem on no-MMU systems,
it is normally safe to say Y here.
See Documentation/nommu-mmap.txt for more information.
config SYSTEM_DATA_VERIFICATION
def_bool n
select SYSTEM_TRUSTED_KEYRING
select KEYS
select CRYPTO
select ASYMMETRIC_KEY_TYPE
select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
select PUBLIC_KEY_ALGO_RSA
select ASN1
select OID_REGISTRY
select X509_CERTIFICATE_PARSER
select PKCS7_MESSAGE_PARSER
help
Provide PKCS#7 message verification using the contents of the system
trusted keyring to provide public keys. This then can be used for
module verification, kexec image verification and firmware blob
verification.
config PROFILING
bool "Profiling support"
help
Say Y here to enable the extended profiling support mechanisms used
by profilers such as OProfile.
#
# Place an empty function call at each tracepoint site. Can be
# dynamically changed for a probe function.
#
config TRACEPOINTS
bool
source "arch/Kconfig"
endmenu # General setup
config HAVE_GENERIC_DMA_COHERENT
bool
default n
config SLABINFO
bool
depends on PROC_FS
depends on SLAB || SLUB_DEBUG
default y
config RT_MUTEXES
bool
config BASE_SMALL
int
default 0 if BASE_FULL
default 1 if !BASE_FULL
menuconfig MODULES
bool "Enable loadable module support"
option modules
help
Kernel modules are small pieces of compiled code which can
be inserted in the running kernel, rather than being
permanently built into the kernel. You use the "modprobe"
tool to add (and sometimes remove) them. If you say Y here,
many parts of the kernel can be built as modules (by
answering M instead of Y where indicated): this is most
useful for infrequently used options which are not required
for booting. For more information, see the man pages for
modprobe, lsmod, modinfo, insmod and rmmod.
If you say Y here, you will need to run "make
modules_install" to put the modules under /lib/modules/
where modprobe can find them (you may need to be root to do
this).
If unsure, say Y.
if MODULES
config MODULE_FORCE_LOAD
bool "Forced module loading"
default n
help
Allow loading of modules without version information (ie. modprobe
--force). Forced module loading sets the 'F' (forced) taint flag and
is usually a really bad idea.
config MODULE_UNLOAD
bool "Module unloading"
help
Without this option you will not be able to unload any
modules (note that some modules may not be unloadable
anyway), which makes your kernel smaller, faster
and simpler. If unsure, say Y.
config MODULE_FORCE_UNLOAD
bool "Forced module unloading"
depends on MODULE_UNLOAD
help
This option allows you to force a module to unload, even if the
kernel believes it is unsafe: the kernel will remove the module
without waiting for anyone to stop using it (using the -f option to
rmmod). This is mainly for kernel developers and desperate users.
If unsure, say N.
config MODVERSIONS
bool "Module versioning support"
help
Usually, you have to use modules compiled with your kernel.
Saying Y here makes it sometimes possible to use modules
compiled for different kernels, by adding enough information
to the modules to (hopefully) spot any changes which would
make them incompatible with the kernel you are running. If
unsure, say N.
config MODULE_SRCVERSION_ALL
bool "Source checksum for all modules"
help
Modules which contain a MODULE_VERSION get an extra "srcversion"
field inserted into their modinfo section, which contains a
sum of the source files which made it. This helps maintainers
see exactly which source was used to build a module (since
others sometimes change the module source without updating
the version). With this option, such a "srcversion" field
will be created for all modules. If unsure, say N.
config MODULE_SIG
bool "Module signature verification"
depends on MODULES
select SYSTEM_DATA_VERIFICATION
help
Check modules for valid signatures upon load: the signature
is simply appended to the module. For more information see
Documentation/module-signing.txt.
Note that this option adds the OpenSSL development packages as a
kernel build dependency so that the signing tool can use its crypto
library.
!!!WARNING!!! If you enable this option, you MUST make sure that the
module DOES NOT get stripped after being signed. This includes the
debuginfo strip done by some packagers (such as rpmbuild) and
inclusion into an initramfs that wants the module size reduced.
config MODULE_SIG_FORCE
bool "Require modules to be validly signed"
depends on MODULE_SIG
help
Reject unsigned modules or signed modules for which we don't have a
key. Without this, such modules will simply taint the kernel.
config MODULE_SIG_ALL
bool "Automatically sign all modules"
default y
depends on MODULE_SIG
help
Sign all modules during make modules_install. Without this option,
modules must be signed manually, using the scripts/sign-file tool.
comment "Do not forget to sign required modules with scripts/sign-file"
depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
choice
prompt "Which hash algorithm should modules be signed with?"
depends on MODULE_SIG
help
This determines which sort of hashing algorithm will be used during
signature generation. This algorithm _must_ be built into the kernel
directly so that signature verification can take place. It is not
possible to load a signed module containing the algorithm to check
the signature on that module.
config MODULE_SIG_SHA1
bool "Sign modules with SHA-1"
select CRYPTO_SHA1
config MODULE_SIG_SHA224
bool "Sign modules with SHA-224"
select CRYPTO_SHA256
config MODULE_SIG_SHA256
bool "Sign modules with SHA-256"
select CRYPTO_SHA256
config MODULE_SIG_SHA384
bool "Sign modules with SHA-384"
select CRYPTO_SHA512
config MODULE_SIG_SHA512
bool "Sign modules with SHA-512"
select CRYPTO_SHA512
endchoice
config MODULE_SIG_HASH
string
depends on MODULE_SIG
default "sha1" if MODULE_SIG_SHA1
default "sha224" if MODULE_SIG_SHA224
default "sha256" if MODULE_SIG_SHA256
default "sha384" if MODULE_SIG_SHA384
default "sha512" if MODULE_SIG_SHA512
config MODULE_COMPRESS
bool "Compress modules on installation"
depends on MODULES
help
Compresses kernel modules when 'make modules_install' is run; gzip or
xz depending on "Compression algorithm" below.
module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
Out-of-tree kernel modules installed using Kbuild will also be
compressed upon installation.
Note: for modules inside an initrd or initramfs, it's more efficient
to compress the whole initrd or initramfs instead.
Note: This is fully compatible with signed modules.
If in doubt, say N.
choice
prompt "Compression algorithm"
depends on MODULE_COMPRESS
default MODULE_COMPRESS_GZIP
help
This determines which sort of compression will be used during
'make modules_install'.
GZIP (default) and XZ are supported.
config MODULE_COMPRESS_GZIP
bool "GZIP"
config MODULE_COMPRESS_XZ
bool "XZ"
endchoice
endif # MODULES
config MODULES_TREE_LOOKUP
def_bool y
depends on PERF_EVENTS || TRACING
config INIT_ALL_POSSIBLE
bool
help
Back when each arch used to define their own cpu_online_mask and
cpu_possible_mask, some of them chose to initialize cpu_possible_mask
with all 1s, and others with all 0s. When they were centralised,
it was better to provide this option than to break all the archs
and have several arch maintainers pursuing me down dark alleys.
config STOP_MACHINE
bool
default y
depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU
help
Need stop_machine() primitive.
source "block/Kconfig"
config PREEMPT_NOTIFIERS
bool
config PADATA
depends on SMP
bool
# Can be selected by architectures with broken toolchains
# that get confused by correct const<->read_only section
# mappings
config BROKEN_RODATA
bool
config ASN1
tristate
help
Build a simple ASN.1 grammar compiler that produces a bytecode output
that can be interpreted by the ASN.1 stream decoder and used to
inform it as to what tags are to be expected in a stream and what
functions to call on what tags.
source "kernel/Kconfig.locks"
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