icount_warp_rt function is called by qemu_clock_warp and as
callback of icount_warp timer. This patch adds call to qemu_clock_warp
into main_loop_wait function, because icount warp may be missed
in record/replay mode, when CPU is sleeping.
This patch also disables of calling this function by timer, because
it is not needed after making modifications of main_loop_wait.
Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
Message-Id: <20150917162439.8676.38290.stgit@PASHA-ISP.def.inno>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Clock ticks are considered as the sources of non-deterministic data for
virtual machine. This patch implements saving the clock values when they
are acquired (virtual, host clock).
When replaying the execution corresponding values are read from log and
transfered to the module, which wants to read the values.
Such a design required the clock polling to be synchronized. Sometimes
it is not true - e.g. when timeouts for timer lists are checked. In this case
we use a cached value of the clock, passing it to the client code.
Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
Message-Id: <20150917162427.8676.36558.stgit@PASHA-ISP.def.inno>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
This patch adds calls to replay functions into the icount setup block.
In record mode number of executed instructions is written to the log.
In replay mode number of istructions to execute is taken from the replay log.
When replayed instructions counter is expired qemu_notify_event()
function is called to wake up the iothread.
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
Message-Id: <20150917162405.8676.31890.stgit@PASHA-ISP.def.inno>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This should help clarify the purpose of the function that returns
the host system's CPU cycle count.
Signed-off-by: Christopher Covington <cov@codeaurora.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
ppc portion
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Provide a method to throttle guest cpu execution. CPUState is augmented with
timeout controls and throttle start/stop functions. To throttle the guest cpu
the caller simply has to call the throttle set function and provide a percentage
of throttle time.
Signed-off-by: Jason J. Herne <jjherne@linux.vnet.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.vnet.ibm.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
This hides the tcg_halt_cond and tcg_cpu_thread global variables
inside qemu_tcg_init_vcpu. Multi-threaded TCG will need one
QemuCond and one QemuThread per virtual cpu, so it's preferrable
to use cpu->halt_cond and cpu->thread.
Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
Message-Id: <1439220437-23957-9-git-send-email-fred.konrad@greensocs.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Protect the list of queued work items with something other than
the BQL, as a preparation for running the work items outside it.
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signals are slow and do not exist on Win32. The previous patches
have done most of the legwork to introduce memory barriers (some
of them were even there already for the sake of Windows!) and
we can now set the flags directly in the iothread.
qemu_cpu_kick_thread is not used anymore on TCG, since the TCG thread is
never outside usermode while the CPU is running (not halted). Instead run
the content of the signal handler (now in qemu_cpu_kick_no_halt) directly.
qemu_cpu_kick_no_halt is also used in qemu_mutex_lock_iothread to avoid
the overhead of qemu_cond_broadcast.
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Use the same API to trigger interruption of a CPU, no matter if
under TCG or KVM. There is no difference: these calls come from
the CPU thread, so the qemu_cpu_kick calls will send a signal
to the running thread and it will be processed synchronously,
just like a call to cpu_exit. The only difference is in the
overhead, but neither call to cpu_exit (now qemu_cpu_kick)
is in a hot path.
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Synchronize the remaining pair of accesses in cpu_signal. These should
be necessary on Windows as well, at least in theory. Probably
SuspendProcess and ResumeProcess introduce some implicit memory
barrier.
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This is already useful on Windows in order to remove tls.h, because
accesses to current_cpu are done from a different thread on that
platform. It will be used on POSIX platforms as soon TCG stops using
signals to interrupt the execution of translated code.
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
When QEMU starts the RCU thread executes qemu_mutex_lock_thread
causing error "qemu:qemu_cpu_kick_thread: No such process" and exits.
This isn't occur frequently but in glibc the thread id can exist and
this not guarantee that the thread is on active/running state. If is
inserted a sleep(1) after newthread assignment [1] the issue appears.
So not make assumption that thread exist if first_cpu->thread is set
then change the validation of cpu to created that is set into cpu
threads (kvm, tcg, dummy).
[1] https://sourceware.org/git/?p=glibc.git;a=blob;f=nptl/pthread_create.c;h=d10f4ea8004e1d8f3a268b95cc0f8d93b8d89867;hb=HEAD#l621
Cc: qemu-stable@nongnu.org
Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com>
Message-Id: <1441313313-3040-1-git-send-email-anibal.limon@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
After commit 626cf8f (icount: set can_do_io outside TB execution,
2014-12-08), can_do_io is set to 1 if not executing code. It is
no longer necessary to make this assumption in cpu_can_do_io.
It is also possible to remove the use_icount test, simply by
never setting cpu->can_do_io to 0 unless use_icount is true.
With these changes cpu_can_do_io boils down to a read of
cpu->can_do_io.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Remove un-needed usages of ENV_GET_CPU() by converting the APIs to use
CPUState pointers and retrieving the env_ptr as minimally needed.
Scripted conversion for target-* change:
for I in target-*/cpu.h; do
sed -i \
's/\(^int cpu_[^_]*_exec(\)[^ ][^ ]* \*s);$/\1CPUState *cpu);/' \
$I;
done
Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
The sole caller of this function navigates the cpu->env_ptr only for
this function to take it back the cpu pointer straight away. Pass in
cpu pointer instead and grab the env pointer locally in the function.
Removes a core code usage of ENV_GET_CPU().
Reviewed-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
This function will be used to avoid recursive locking of the iothread lock
whenever address_space_rw/ld*/st* are called with the BQL held, which is
almost always the case.
Tracking whether the iothread is owned is very cheap (just use a TLS
variable) but requires some care because now the lock must always be
taken with qemu_mutex_lock_iothread(). Previously this wasn't the case.
Outside TCG mode this is not a problem. In TCG mode, we need to be
careful and avoid the "prod out of compiled code" step if already
in a VCPU thread. This is easily done with a check on current_cpu,
i.e. qemu_in_vcpu_thread().
Hopefully, multithreaded TCG will get rid of the whole logic to kick
VCPUs whenever an I/O event occurs!
Cc: Frederic Konrad <fred.konrad@greensocs.com>
Message-Id: <1434646046-27150-3-git-send-email-pbonzini@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The next patch will require the BQL to be always taken with
qemu_mutex_lock_iothread(), while right now this isn't the case.
Outside TCG mode this is not a problem. In TCG mode, we need to be
careful and avoid the "prod out of compiled code" step if already
in a VCPU thread. This is easily done with a check on current_cpu,
i.e. qemu_in_vcpu_thread().
Hopefully, multithreaded TCG will get rid of the whole logic to kick
VCPUs whenever an I/O event occurs!
Cc: Frederic Konrad <fred.konrad@greensocs.com>
Message-Id: <1434646046-27150-2-git-send-email-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
These macros expand into error class enumeration constant, comma,
string. Unclean. Has been that way since commit 13f59ae.
The error class is always ERROR_CLASS_GENERIC_ERROR since the previous
commit.
Clean up as follows:
* Prepend every use of a QERR_ macro by ERROR_CLASS_GENERIC_ERROR, and
delete it from the QERR_ macro. No change after preprocessing.
* Rewrite error_set(ERROR_CLASS_GENERIC_ERROR, ...) into
error_setg(...). Again, no change after preprocessing.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Luiz Capitulino <lcapitulino@redhat.com>
We create optional sections with this patch. But we already have
optional subsections. Instead of having two mechanism that do the
same, we can just generalize it.
For subsections we just change:
- Add a needed function to VMStateDescription
- Remove VMStateSubsection (after removal of the needed function
it is just a VMStateDescription)
- Adjust the whole tree, moving the needed function to the corresponding
VMStateDescription
Signed-off-by: Juan Quintela <quintela@redhat.com>
While qemu is running in sleep=no mode, a warning will be printed
when no timer deadline is set.
As this mode is intended for getting deterministic virtual time, if no
timer is set on the virtual clock this determinism is broken.
Signed-off-by: Victor CLEMENT <victor.clement@openwide.fr>
Message-Id: <1432912446-9811-4-git-send-email-victor.clement@openwide.fr>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The 'sleep' parameter sets the icount_sleep mode, which is enabled by
default. To disable it, add the 'sleep=no' parameter (or 'nosleep') to the
qemu -icount option.
Signed-off-by: Victor CLEMENT <victor.clement@openwide.fr>
Message-Id: <1432912446-9811-3-git-send-email-victor.clement@openwide.fr>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
When the icount_sleep mode is disabled, the QEMU_VIRTUAL_CLOCK runs at the
maximum possible speed by warping the sleep times of the virtual cpu to the
soonest clock deadline. The virtual clock will be updated only according
the instruction counter.
Signed-off-by: Victor CLEMENT <victor.clement@openwide.fr>
Message-Id: <1432912446-9811-2-git-send-email-victor.clement@openwide.fr>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This will allow clients to query additional information directly using
qom-get on the CPU objects.
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
following a464982499, it's now possible for
there to be attempts to take the BQL before CPUs have been realized in
cases where a machine model inits peripherals before the first CPU.
BQL lock aquisition kicks the first_cpu, leading to a segfault if this
happens pre-realize. Guard the CPU kick routine to perform no action for
a CPU that doesn't exist or doesn't have a thread yet.
There was a fix to this with commit
6b49809c59, but the check there misses
the case where the CPU has been inited and not realized. Strengthen the
check to make sure that the first_cpu has a thread (i.e. it is
realized) before allowing the kick.
Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Message-Id: <1427107689-6946-1-git-send-email-peter.crosthwaite@xilinx.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2ed1ebcf6 "timer: replace time() with QEMU_CLOCK_HOST" broke compile
when configured with --enable-profiler. Turned out the profiler has been
broken for a while.
This does s/qemu_time/tcg_time/ as the profiler only works in a TCG mode.
This also fixes the compile error.
This changes profile_getclock() to return nanoseconds rather than
CPU ticks as the "profile" HMP command prints seconds and there is no
platform-independent way to get ticks-per-second rate.
Since TCG is quite slow and get_clock() returns nanoseconds (fine
enough), this should not affect precision much.
This removes unused qemu_time_start and tlb_flush_time.
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Message-Id: <1426478258-29961-1-git-send-email-aik@ozlabs.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
When requesting a size which cannot be read, the error message shows
a different address which is misleading to the user and it looks like
something's wrong with the address parsing. This is because the input
@addr variable is incremented in the memory dumping loop:
(qemu) memsave 0xffffffff8418069c 0xb00000 mem
Invalid addr 0xffffffff849ffe9c specified
Fix that by saving the original address and size and use them in the
error message:
(qemu) memsave 0xffffffff8418069c 0xb00000 mem
Invalid addr 0xffffffff8418069c/size 11534336 specified
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
For good measure, ensure that the following sequence:
thread 1 calls qemu_mutex_lock_iothread
thread 2 calls qemu_mutex_lock_iothread
VCPU thread are created
VCPU thread enters execution loop
results in the VCPU threads letting the other two threads run
and obeying iothread_requesting_mutex even if the VCPUs are
not halted. To do this, check iothread_requesting_mutex
before execution starts.
Tested-by: Leon Alrae <leon.alrae@imgtec.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
When two threads (other than the low-priority TCG VCPU thread)
are competing for the iothread lock, a deadlock can happen. This
is because iothread_requesting_mutex is set to false by the first
thread that gets the mutex, and then the VCPU thread might never
yield from the execution loop. If iothread_requesting_mutex is
changed from a bool to a counter, the deadlock is fixed.
However, there is another bug in qemu_mutex_lock_iothread that
can be triggered by the new call_rcu thread. The bug happens
if qemu_mutex_lock_iothread is called before the CPUs are
created. In that case, first_cpu is NULL and the caller
segfaults in qemu_mutex_lock_iothread. To fix this, just
do not do the kick if first_cpu is NULL.
Reported-by: Leon Alrae <leon.alrae@imgtec.com>
Reported-by: Andreas Gustafsson <gson@gson.org>
Tested-by: Leon Alrae <leon.alrae@imgtec.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
- RCU: fix MemoryRegion lifetime issues in PCI; document the rules;
convert of AddressSpaceDispatch and RAMList
- KVM: add kvm_exit reasons for aarch64
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Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging
- vhost-scsi: add bootindex property
- RCU: fix MemoryRegion lifetime issues in PCI; document the rules;
convert of AddressSpaceDispatch and RAMList
- KVM: add kvm_exit reasons for aarch64
# gpg: Signature made Mon Feb 16 16:32:32 2015 GMT using RSA key ID 78C7AE83
# gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>"
# gpg: aka "Paolo Bonzini <pbonzini@redhat.com>"
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg: There is no indication that the signature belongs to the owner.
# Primary key fingerprint: 46F5 9FBD 57D6 12E7 BFD4 E2F7 7E15 100C CD36 69B1
# Subkey fingerprint: F133 3857 4B66 2389 866C 7682 BFFB D25F 78C7 AE83
* remotes/bonzini/tags/for-upstream: (21 commits)
Convert ram_list to RCU
exec: convert ram_list to QLIST
cosmetic changes preparing for the following patches
exec: protect mru_block with RCU
rcu: add g_free_rcu
rcu: introduce RCU-enabled QLIST
exec: RCUify AddressSpaceDispatch
exec: make iotlb RCU-friendly
exec: introduce cpu_reload_memory_map
docs: clarify memory region lifecycle
pci: split shpc_cleanup and shpc_free
pcie: remove mmconfig memory leak and wrap mmconfig update with transaction
memory: keep the owner of the AddressSpace alive until do_address_space_destroy
rcu: run RCU callbacks under the BQL
rcu: do not let RCU callbacks pile up indefinitely
vhost-scsi: set the bootable value of channel/target/lun
vhost-scsi: add a property for booting
vhost-scsi: expose the TYPE_FW_PATH_PROVIDER interface
vhost-scsi: add bootindex property
qdev: support to get a device firmware path directly
...
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Note that even after this patch, most callers of address_space_*
functions must still be under the big QEMU lock, otherwise the memory
region returned by address_space_translate can disappear as soon as
address_space_translate returns. This will be fixed in the next part
of this series.
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
qemu_clock_run_timers() only takes care of main_loop_tlg, we shouldn't
forget aio timer list groups.
Currently, the qemu_clock_deadline_ns_all (a few lines above) counts all
the timergroups of this clock type, including aio tlg, but we don't fire
them, so they are never cleared, which makes a dead loop.
For example, this function hangs when trying to drive throttled block
request queue with qtest clock_step.
Signed-off-by: Fam Zheng <famz@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1421661103-29153-1-git-send-email-famz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
With the introduction of QEMU_CLOCK_VIRTUAL_RT, the computation of
sc->diff_clk can be simplified nicely:
qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) -
qemu_clock_get_ns(QEMU_CLOCK_REALTIME) +
cpu_get_clock_offset()
= qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) -
(qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - cpu_get_clock_offset())
= qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) -
(qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + timers_state.cpu_clock_offset)
= qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) -
qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT)
Cc: Sebastian Tanase <sebastian.tanase@openwide.fr>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Fix mismatch between timer_new_ms and timer_mod.
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This patch makes icount warp use the new QEMU_CLOCK_VIRTUAL_RT clock.
This way, icount's QEMU_CLOCK_VIRTUAL will never count time during which
the virtual machine is stopped.
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Separate accessing the instruction counter from the compensation for
speed and halting that are introduced by qemu_icount_bias. This
introduces new infrastructure used by the record/replay patches.
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This patch sets can_do_io function to allow reading icount
within cpu-exec, but outside TB execution.
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Exception index is reset at every entry at every entry into cpu_exec()
function. This may cause missing the exceptions while replaying them.
This patch moves exception_index reset to the locations where they are
processed.
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Ticks and clock offset used by CPU timers have to be saved in vmstate.
But vmstate for these fields registered only in icount mode.
Missing registration leads to breaking the continuity when vmstate is loaded.
This patch introduces new initialization function which fixes this.
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This implements an NMI interface for s390 and s390-ccw machines.
This removes #ifdef s390 branch in qmp_inject_nmi so new s390's
nmi_monitor_handler() callback is going to be used for NMI.
Since nmi_monitor_handler()-calling code is platform independent,
CPUState::cpu_index is used instead of S390CPU::env.cpu_num.
There should not be any change in behaviour as both @cpu_index and
@cpu_num are global CPU numbers.
Note that s390_cpu_restart() already takes care of the specified cpu,
so we don't need to schedule via async_run_on_cpu().
Since the only error s390_cpu_restart() can return is ENOSYS, convert
it to QERR_UNSUPPORTED.
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This introduces an NMI (Non Maskable Interrupt) interface with
a single nmi_monitor_handler() method. A machine or a device can
implement it. This searches for an QOM object with this interface
and if it is implemented, calls it. The callback implements an action
required to cause debug crash dump on in-kernel debugger invocation.
The callback returns Error**.
This adds a nmi_monitor_handle() helper which walks through
all objects to find the interface. The interface method is called
for all found instances.
This adds support for it in qmp_inject_nmi(). Since no architecture
supports it at the moment, there is no change in behaviour.
This changes inject-nmi command description for HMP and QMP.
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Show in 'info jit' the current delay between the host clock
and the guest clock. In addition, print the maximum advance
and delay of the guest compared to the host.
Signed-off-by: Sebastian Tanase <sebastian.tanase@openwide.fr>
Tested-by: Camille Bégué <camille.begue@openwide.fr>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The goal is to sleep qemu whenever the guest clock
is in advance compared to the host clock (we use
the monotonic clocks). The amount of time to sleep
is calculated in the execution loop in cpu_exec.
At first, we tried to approximate at each for loop the real time elapsed
while searching for a TB (generating or retrieving from cache) and
executing it. We would then approximate the virtual time corresponding
to the number of virtual instructions executed. The difference between
these 2 values would allow us to know if the guest is in advance or delayed.
However, the function used for measuring the real time
(qemu_clock_get_ns(QEMU_CLOCK_REALTIME)) proved to be very expensive.
We had an added overhead of 13% of the total run time.
Therefore, we modified the algorithm and only take into account the
difference between the 2 clocks at the begining of the cpu_exec function.
During the for loop we try to reduce the advance of the guest only by
computing the virtual time elapsed and sleeping if necessary. The overhead
is thus reduced to 3%. Even though this method still has a noticeable
overhead, it no longer is a bottleneck in trying to achieve a better
guest frequency for which the guest clock is faster than the host one.
As for the the alignement of the 2 clocks, with the first algorithm
the guest clock was oscillating between -1 and 1ms compared to the host clock.
Using the second algorithm we notice that the guest is 5ms behind the host, which
is still acceptable for our use case.
The tests where conducted using fio and stress. The host machine in an i5 CPU at
3.10GHz running Debian Jessie (kernel 3.12). The guest machine is an arm versatile-pb
built with buildroot.
Currently, on our test machine, the lowest icount we can achieve that is suitable for
aligning the 2 clocks is 6. However, we observe that the IO tests (using fio) are
slower than the cpu tests (using stress).
Signed-off-by: Sebastian Tanase <sebastian.tanase@openwide.fr>
Tested-by: Camille Bégué <camille.begue@openwide.fr>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The align option is used for activating the align algorithm
in order to synchronise the host clock and the guest clock.
Signed-off-by: Sebastian Tanase <sebastian.tanase@openwide.fr>
Tested-by: Camille Bégué <camille.begue@openwide.fr>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Make icount parameter use QemuOpts style options in order
to easily add other suboptions.
Signed-off-by: Sebastian Tanase <sebastian.tanase@openwide.fr>
Tested-by: Camille Bégué <camille.begue@openwide.fr>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
