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68d124b099
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Paul E. McKenney 68d124b099 rcu: Add rcutree.nohz_full_patience_delay to reduce nohz_full OS jitter 
If a CPU is running either a userspace application or a guest OS in
nohz_full mode, it is possible for a system call to occur just as an
RCU grace period is starting.  If that CPU also has the scheduling-clock
tick enabled for any reason (such as a second runnable task), and if the
system was booted with rcutree.use_softirq=0, then RCU can add insult to
injury by awakening that CPU's rcuc kthread, resulting in yet another
task and yet more OS jitter due to switching to that task, running it,
and switching back.

In addition, in the common case where that system call is not of
excessively long duration, awakening the rcuc task is pointless.
This pointlessness is due to the fact that the CPU will enter an extended
quiescent state upon returning to the userspace application or guest OS.
In this case, the rcuc kthread cannot do anything that the main RCU
grace-period kthread cannot do on its behalf, at least if it is given
a few additional milliseconds (for example, given the time duration
specified by rcutree.jiffies_till_first_fqs, give or take scheduling
delays).

This commit therefore adds a rcutree.nohz_full_patience_delay kernel
boot parameter that specifies the grace period age (in milliseconds,
rounded to jiffies) before which RCU will refrain from awakening the
rcuc kthread.  Preliminary experimentation suggests a value of 1000,
that is, one second.  Increasing rcutree.nohz_full_patience_delay will
increase grace-period latency and in turn increase memory footprint,
so systems with constrained memory might choose a smaller value.
Systems with less-aggressive OS-jitter requirements might choose the
default value of zero, which keeps the traditional immediate-wakeup
behavior, thus avoiding increases in grace-period latency.

[ paulmck: Apply Leonardo Bras feedback.  ]

Link: https://lore.kernel.org/all/20240328171949.743211-1-leobras@redhat.com/

Reported-by: Leonardo Bras <leobras@redhat.com>
Suggested-by: Leonardo Bras <leobras@redhat.com>
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Leonardo Bras <leobras@redhat.com>
2024-07-04 13:47:39 -07:00
..
bpf The usual shower of singleton fixes and minor series all over MM, 2024-05-19 09:21:03 -07:00
cgroup Misc fixes: 2024-05-19 11:38:15 -07:00
configs hardening updates for 6.10-rc1 2024-05-13 14:14:05 -07:00
debug kdb: Simplify management of tmpbuffer in kdb_read() 2024-04-26 17:13:31 +01:00
dma dma-mapping updates for Linux 6.10 2024-05-20 10:23:39 -07:00
entry entry: Respect changes to system call number by trace_sys_enter() 2024-03-12 13:23:32 +01:00
events The usual shower of singleton fixes and minor series all over MM, 2024-05-19 09:21:03 -07:00
futex printk: Change type of CONFIG_BASE_SMALL to bool 2024-05-06 17:39:09 +02:00
gcov gcov: annotate struct gcov_iterator with __counted_by 2023-10-18 14:43:22 -07:00
irq genirq/irqdesc: Prevent use-after-free in irq_find_at_or_after() 2024-05-24 12:49:35 +02:00
kcsan kcsan, compiler_types: Introduce __data_racy type qualifier 2024-05-07 11:39:50 -07:00
livepatch livepatch: Rename KLP_* to KLP_TRANSITION_* 2024-05-09 15:48:01 +02:00
locking - Core Frameworks 2024-05-22 10:49:54 -07:00
module Driver core changes for 6.10-rc1 2024-05-22 12:13:40 -07:00
power getting rid of bogus set_blocksize() uses, switching it 2024-05-21 08:34:51 -07:00
printk TTY/Serial changes for 6.10-rc1 2024-05-22 11:53:02 -07:00
rcu rcu: Add rcutree.nohz_full_patience_delay to reduce nohz_full OS jitter 2024-07-04 13:47:39 -07:00
sched bitmap patches for 6.10 2024-05-21 15:29:01 -07:00
time sysctl changes for v6.10-rc1 2024-05-17 17:31:24 -07:00
trace tracing: Minor last minute fixes 2024-05-23 12:36:38 -07:00
.gitignore
acct.c kernel misc: Remove the now superfluous sentinel elements from ctl_table array 2024-04-24 09:43:53 +02:00
async.c async: Use a dedicated unbound workqueue with raised min_active 2024-02-09 11:13:59 -10:00
audit_fsnotify.c
audit_tree.c fsnotify: create a wrapper fsnotify_find_inode_mark() 2024-04-04 16:24:16 +02:00
audit_watch.c fsnotify: create a wrapper fsnotify_find_inode_mark() 2024-04-04 16:24:16 +02:00
audit.c audit: use KMEM_CACHE() instead of kmem_cache_create() 2024-01-25 10:12:22 -05:00
audit.h audit: correct audit_filter_inodes() definition 2023-07-21 12:17:25 -04:00
auditfilter.c audit: remove unnecessary assignment in audit_dupe_lsm_field() 2024-01-25 09:59:27 -05:00
auditsc.c audit,io_uring: io_uring openat triggers audit reference count underflow 2023-10-13 18:34:46 +02:00
backtracetest.c backtracetest: Convert from tasklet to BH workqueue 2024-02-05 13:22:34 -10:00
bounds.c bounds: Use the right number of bits for power-of-two CONFIG_NR_CPUS 2024-04-29 08:29:29 -07:00
capability.c lsm: constify the 'target' parameter in security_capget() 2023-08-08 16:48:47 -04:00
cfi.c
compat.c
configs.c
context_tracking.c context_tracking: Make context_tracking_key __ro_after_init 2024-03-22 11:18:18 +01:00
cpu_pm.c
cpu.c cgroup: Changes for v6.10 2024-05-15 17:06:08 -07:00
crash_core.c Mainly singleton patches, documented in their respective changelogs. 2024-05-19 14:02:03 -07:00
crash_reserve.c crash: add prefix for crash dumping messages 2024-05-08 08:41:26 -07:00
cred.c cred: Use KMEM_CACHE() instead of kmem_cache_create() 2024-02-23 17:33:31 -05:00
delayacct.c delayacct: Remove the now superfluous sentinel elements from ctl_table array 2024-04-24 09:43:54 +02:00
dma.c
elfcorehdr.c crash: remove dependency of FA_DUMP on CRASH_DUMP 2024-02-23 17:48:22 -08:00
exec_domain.c
exit.c virtio: features, fixes, cleanups 2024-05-23 12:04:36 -07:00
exit.h exit: add internal include file with helpers 2023-09-21 12:03:50 -06:00
extable.c
fail_function.c
fork.c mm: rename mm_put_huge_zero_page to mm_put_huge_zero_folio 2024-04-25 20:56:20 -07:00
freezer.c Linux 6.7-rc6 2023-12-23 15:52:13 +01:00
gen_kheaders.sh
groups.c groups: Convert group_info.usage to refcount_t 2023-09-29 11:28:39 -07:00
hung_task.c kernel misc: Remove the now superfluous sentinel elements from ctl_table array 2024-04-24 09:43:53 +02:00
iomem.c kernel/iomem.c: remove __weak ioremap_cache helper 2023-08-21 13:37:28 -07:00
irq_work.c
jump_label.c jump_label,module: Don't alloc static_key_mod for __ro_after_init keys 2024-03-22 11:18:16 +01:00
kallsyms_internal.h kallsyms: Avoid weak references for kallsyms symbols 2024-05-02 19:48:26 +09:00
kallsyms_selftest.c mm: vmalloc: enable memory allocation profiling 2024-04-25 20:55:57 -07:00
kallsyms_selftest.h
kallsyms.c kallsyms: Avoid weak references for kallsyms symbols 2024-05-02 19:48:26 +09:00
kcmp.c file: convert to SLAB_TYPESAFE_BY_RCU 2023-10-19 11:02:48 +02:00
Kconfig.freezer
Kconfig.hz
Kconfig.kexec crash: clean up kdump related config items 2024-02-23 17:48:22 -08:00
Kconfig.locks
Kconfig.preempt
kcov.c kcov: avoid clang out-of-range warning 2024-04-25 21:07:04 -07:00
kexec_core.c kernel misc: Remove the now superfluous sentinel elements from ctl_table array 2024-04-24 09:43:53 +02:00
kexec_elf.c
kexec_file.c crash: add a new kexec flag for hotplug support 2024-04-23 14:59:01 +10:00
kexec_internal.h crash: remove dependency of FA_DUMP on CRASH_DUMP 2024-02-23 17:48:22 -08:00
kexec.c crash: add a new kexec flag for hotplug support 2024-04-23 14:59:01 +10:00
kheaders.c
kprobes.c kprobe/ftrace: fix build error due to bad function definition 2024-05-17 19:17:55 -07:00
ksyms_common.c
ksysfs.c vmlinux: Avoid weak reference to notes section 2024-05-02 19:48:26 +09:00
kthread.c kunit: Handle test faults 2024-05-06 14:22:02 -06:00
latencytop.c kernel misc: Remove the now superfluous sentinel elements from ctl_table array 2024-04-24 09:43:53 +02:00
Makefile crash: split crash dumping code out from kexec_core.c 2024-02-23 17:48:22 -08:00
module_signature.c
notifier.c
nsproxy.c pidfd: add pidfs 2024-03-01 12:23:37 +01:00
numa.c kernel/numa.c: Move logging out of numa.h 2023-12-20 19:26:30 -05:00
padata.c padata: Disable BH when taking works lock on MT path 2024-04-12 15:07:51 +08:00
panic.c kernel misc: Remove the now superfluous sentinel elements from ctl_table array 2024-04-24 09:43:53 +02:00
params.c params: Fix multi-line comment style 2023-12-01 09:51:44 -08:00
pid_namespace.c kernel misc: Remove the now superfluous sentinel elements from ctl_table array 2024-04-24 09:43:53 +02:00
pid_sysctl.h kernel misc: Remove the now superfluous sentinel elements from ctl_table array 2024-04-24 09:43:53 +02:00
pid.c pidfs: remove config option 2024-03-13 12:53:53 -07:00
profile.c profiling: Remove create_prof_cpu_mask(). 2024-04-27 11:17:48 -07:00
ptrace.c ptrace_attach: shift send(SIGSTOP) into ptrace_set_stopped() 2024-02-22 15:38:52 -08:00
range.c
reboot.c kernel misc: Remove the now superfluous sentinel elements from ctl_table array 2024-04-24 09:43:53 +02:00
regset.c regset: use kvzalloc() for regset_get_alloc() 2024-04-25 21:07:03 -07:00
relay.c kernel: relay: remove relay_file_splice_read dead code, doesn't work 2023-12-29 12:22:27 -08:00
resource_kunit.c
resource.c Quite a lot of kexec work this time around. Many singleton patches in 2024-01-09 11:46:20 -08:00
rseq.c
scftorture.c scftorture: Pause testing after memory-allocation failure 2023-07-14 15:02:57 -07:00
scs.c
seccomp.c sysctl changes for v6.10-rc1 2024-05-17 17:31:24 -07:00
signal.c virtio: features, fixes, cleanups 2024-05-23 12:04:36 -07:00
smp.c CSD lock commits for v6.7 2023-10-30 17:56:53 -10:00
smpboot.c kthread: add kthread_stop_put 2023-10-04 10:41:57 -07:00
smpboot.h
softirq.c softirq: Fix suspicious RCU usage in __do_softirq() 2024-04-29 05:03:51 +02:00
stackleak.c sysctl changes for v6.10-rc1 2024-05-17 17:31:24 -07:00
stacktrace.c stacktrace: fix kernel-doc typo 2023-12-29 12:22:29 -08:00
static_call_inline.c
static_call.c
stop_machine.c
sys_ni.c mseal: wire up mseal syscall 2024-05-23 19:40:26 -07:00
sys.c RISC-V Patches for the 6.10 Merge Window, Part 1 2024-05-22 09:56:00 -07:00
sysctl-test.c
sysctl.c kernel misc: Remove the now superfluous sentinel elements from ctl_table array 2024-04-24 09:43:53 +02:00
task_work.c task_work: add kerneldoc annotation for 'data' argument 2023-09-19 13:21:32 -07:00
taskstats.c taskstats: fill_stats_for_tgid: use for_each_thread() 2023-10-04 10:41:57 -07:00
torture.c torture: Print out torture module parameters 2023-09-24 17:24:01 +02:00
tracepoint.c
tsacct.c
ucount.c sysctl changes for v6.10-rc1 2024-05-17 17:31:24 -07:00
uid16.c
uid16.h
umh.c umh: Remove the now superfluous sentinel elements from ctl_table array 2024-04-24 09:43:53 +02:00
up.c smp: Change function signatures to use call_single_data_t 2023-09-13 14:59:24 +02:00
user_namespace.c user_namespace: remove unnecessary NULL values from kbuf 2024-02-22 15:38:52 -08:00
user-return-notifier.c
user.c printk: Change type of CONFIG_BASE_SMALL to bool 2024-05-06 17:39:09 +02:00
usermode_driver.c
utsname_sysctl.c kernel misc: Remove the now superfluous sentinel elements from ctl_table array 2024-04-24 09:43:53 +02:00
utsname.c
vhost_task.c vhost_task: Handle SIGKILL by flushing work and exiting 2024-05-22 08:31:15 -04:00
vmcore_info.c mm: free up PG_slab 2024-04-25 20:56:00 -07:00
watch_queue.c watch_queue: fix kcalloc() arguments order 2023-12-21 13:17:54 +01:00
watchdog_buddy.c watchdog/hardlockup: move SMP barriers from common code to buddy code 2023-06-19 16:25:28 -07:00
watchdog_perf.c kernel/watchdog_perf.c: tidy up kerneldoc 2024-05-08 08:41:29 -07:00
watchdog.c Mainly singleton patches, documented in their respective changelogs. 2024-05-19 14:02:03 -07:00
workqueue_internal.h workqueue: Drop the special locking rule for worker->flags and worker_pool->flags 2023-08-07 15:57:22 -10:00
workqueue.c Merge branch 'for-6.10' into test-merge-for-6.10 2024-05-15 11:40:33 -10:00