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1b022b8763
linux/kernel
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Frederic Weisbecker 1b022b8763 rcu/nocb: Conditionally wake up rcuo if not already waiting on GP 
A callback enqueuer currently wakes up the rcuo kthread if it is adding
the first non-done callback of a CPU, whether the kthread is waiting on
a grace period or not (unless the CPU is offline).

This looks like a desired behaviour because then the rcuo kthread
doesn't wait for the end of the current grace period to handle the
callback. It is accelerated right away and assigned to the next grace
period. The GP kthread is notified about that fact and iterates with
the upcoming GP without sleeping in-between.

However this best-case scenario is contradicted by a few details,
depending on the situation:

1) If the callback is a non-bypass one queued with IRQs enabled, the
   wake up only occurs if no other pending callbacks are on the list.
   Therefore the theoretical "optimization" actually applies on rare
   occasions.

2) If the callback is a non-bypass one queued with IRQs disabled, the
   situation is similar with even more uncertainty due to the deferred
   wake up.

3) If the callback is lazy, a few jiffies don't make any difference.

4) If the callback is bypass, the wake up timer is programmed 2 jiffies
   ahead by rcuo in case the regular pending queue has been handled
   in the meantime. The rare storm of callbacks can otherwise wait for
   the currently elapsing grace period to be flushed and handled.

For all those reasons, the optimization is only theoretical and
occasional. Therefore it is reasonable that callbacks enqueuers only
wake up the rcuo kthread when it is not already waiting on a grace
period to complete.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
2024-09-09 00:05:26 +05:30
..
bpf sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
cgroup Merge branch 'for-6.10-fixes' into for-6.11 2024-07-14 18:04:03 -10:00
configs mm/slab: Plumb kmem_buckets into __do_kmalloc_node() 2024-07-03 12:24:19 +02:00
debug kdb: Get rid of redundant kdb_curr_task() 2024-06-21 15:49:29 +01:00
dma dma: fix call order in dmam_free_coherent 2024-07-19 07:27:28 +02:00
entry entry: Respect changes to system call number by trace_sys_enter() 2024-03-12 13:23:32 +01:00
events A lot of networking people were at a conference last week, busy 2024-07-25 13:32:25 -07:00
futex printk: Change type of CONFIG_BASE_SMALL to bool 2024-05-06 17:39:09 +02:00
gcov gcov: add support for GCC 14 2024-06-15 10:43:06 -07:00
irq Switch ARM/ARM64 over to the modern per device MSI domains: 2024-07-22 14:02:19 -07:00
kcsan kcsan: Add missing MODULE_DESCRIPTION() macro 2024-06-06 11:21:14 -07:00
livepatch livepatch: Replace snprintf() with sysfs_emit() 2024-07-02 16:56:18 +02:00
locking bcachefs changes for 6.11-rc1 (version 2) 2024-07-18 17:27:43 -07:00
module bpf-next-for-netdev 2024-07-09 17:01:46 +02:00
power mm: remove the implementation of swap_free() and always use swap_free_nr() 2024-07-03 19:30:01 -07:00
printk trivial printk changes for 6.11 2024-07-25 13:18:41 -07:00
rcu rcu/nocb: Conditionally wake up rcuo if not already waiting on GP 2024-09-09 00:05:26 +05:30
sched sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
time Fixes and minor updates for the timer migration code: 2024-07-27 10:19:55 -07:00
trace sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
.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
auditfilter.c ima: Avoid blocking in RCU read-side critical section 2024-06-13 14:26:50 -04:00
auditsc.c audit,io_uring: io_uring openat triggers audit reference count underflow 2023-10-13 18:34:46 +02:00
backtracetest.c backtracetest: add MODULE_DESCRIPTION() 2024-06-24 22:24:55 -07:00
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
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 - Unrelated x86/cc changes queued here to avoid ugly cross-merges and 2024-07-15 19:36:01 -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: remove header files which are included more than once 2024-06-24 22:25:08 -07:00
cred.c cred: Use KMEM_CACHE() instead of kmem_cache_create() 2024-02-23 17:33:31 -05:00
delayacct.c sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +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 - 875fa64577da ("mm/hugetlb_vmemmap: fix race with speculative PFN 2024-07-21 17:15:46 -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 sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
freezer.c Linux 6.7-rc6 2023-12-23 15:52:13 +01:00
gen_kheaders.sh kheaders: use command -v to test for existence of cpio 2024-05-30 01:13:20 +09:00
groups.c groups: Convert group_info.usage to refcount_t 2023-09-29 11:28:39 -07:00
hung_task.c sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
iomem.c
irq_work.c
jump_label.c jump_label: Simplify and clarify static_key_fast_inc_cpus_locked() 2024-06-11 11:25:24 +02:00
kallsyms_internal.h kallsyms: get rid of code for absolute kallsyms 2024-07-20 16:33:21 +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: get rid of code for absolute kallsyms 2024-07-20 16:33:21 +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: don't lose track of remote references during softirqs 2024-06-15 10:43:08 -07:00
kexec_core.c sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +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 sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
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 sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +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/panic: add verbose logging of kernel taints in backtraces 2024-06-24 22:25:05 -07:00
params.c params: Fix multi-line comment style 2023-12-01 09:51:44 -08:00
pid_namespace.c sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
pid_sysctl.h sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +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: add missing MODULE_DESCRIPTION() 2024-06-28 19:36:30 -07:00
resource.c resource: Export find_resource_space() 2024-05-28 11:14:14 -05:00
rseq.c
scftorture.c scftorture: Make torture_type static 2024-05-30 15:31:51 -07:00
scs.c
seccomp.c sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
signal.c kernel: rerun task_work while freezing in get_signal() 2024-07-11 01:51:44 -06:00
smp.c smp: Add missing destroy_work_on_stack() call in smp_call_on_cpu() 2024-07-10 22:40:39 +02:00
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: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
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 Probes updates for v6.11: 2024-07-18 12:19:20 -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: Add module description to sysctl-testing 2024-06-03 15:20:37 +02:00
sysctl.c sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
task_work.c task_work: Add TWA_NMI_CURRENT as an additional notify mode. 2024-07-09 13:26:34 +02:00
taskstats.c taskstats: fill_stats_for_tgid: use for_each_thread() 2023-10-04 10:41:57 -07:00
torture.c torture: Add MODULE_DESCRIPTION() 2024-05-30 15:31:38 -07:00
tracepoint.c
tsacct.c tsacct: replace strncpy() with strscpy() 2024-07-12 16:39:53 -07:00
ucount.c sysctl changes for v6.10-rc1 2024-05-17 17:31:24 -07:00
uid16.c
uid16.h
umh.c sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +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 sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +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 kallsyms: get rid of code for absolute kallsyms 2024-07-20 16:33:21 +09:00
watch_queue.c watch_queue: fix kcalloc() arguments order 2023-12-21 13:17:54 +01:00
watchdog_buddy.c
watchdog_perf.c watchdog/perf: properly initialize the turbo mode timestamp and rearm counter 2024-07-17 21:11:34 -07:00
watchdog.c sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
workqueue_internal.h
workqueue.c workqueue: Remove unneeded lockdep_assert_cpus_held() 2024-07-15 14:01:14 -10:00