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Paul E. McKenney 2da4b2a7fd srcu: Expedite first synchronize_srcu() when idle 
Classic SRCU in effect expedites the first synchronize_srcu() when SRCU
is idle, and Mike Galbraith demonstrated that some use cases do in fact
rely on this behavior.  In particular, Mike showed that Steven Rostedt's
hotplug stress script takes 55 seconds with Classic SRCU and more than
16 -minutes- when running Tree SRCU.  Assuming that each Tree SRCU's call
to synchronize_srcu() takes four milliseconds, this implies that Steven's
test invokes synchronize_srcu() in isolation, but more than once per
200 microseconds.  Mike used ftrace to demonstrate that the time between
successive calls to synchronize_srcu() ranged from 118 to 342 microseconds,
with one outlier at 80 milliseconds.  This data clearly indicates that
Tree SRCU needs to expedite the first invocation of synchronize_srcu()
during an SRCU idle period.

This commit therefor introduces a srcu_might_be_idle() function that
probabilistically checks whether or not SRCU is idle.  This function is
used by synchronize_rcu() as an additional criterion in deciding whether
or not to expedite.

(Hat trick to Peter Zijlstra for his earlier suggestion that this might
in fact be a problem.  Which for all I know might have motivated Mike to
look into it.)

Reported-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Mike Galbraith <efault@gmx.de>
2017-04-26 16:32:16 -07:00
..
bpf bpf: fix checking xdp_adjust_head on tail calls 2017-04-17 15:51:57 -04:00
cgroup Merge branch 'for-4.11-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup 2017-04-16 11:48:10 -07:00
configs config: android-base: enable hardened usercopy and kernel ASLR 2017-02-27 18:43:46 -08:00
debug sched/headers: Prepare for new header dependencies before moving code to <linux/sched/debug.h> 2017-03-02 08:42:34 +01:00
events Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-03-17 13:59:52 -07:00
gcov gcov: add support for gcc version >= 6 2016-07-15 14:54:27 +09:00
irq irq/affinity: Fix extra vecs calculation 2017-04-13 23:41:00 +02:00
livepatch livepatch/module: make TAINT_LIVEPATCH module-specific 2016-08-26 14:42:08 +02:00
locking Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu 2017-04-23 11:12:44 +02:00
power Merge branch 'WIP.sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-03-03 10:16:38 -08:00
printk sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task_stack.h> 2017-03-02 08:42:36 +01:00
rcu srcu: Expedite first synchronize_srcu() when idle 2017-04-26 16:32:16 -07:00
sched Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu 2017-04-23 11:12:44 +02:00
time Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-03-07 14:45:22 -08:00
trace ring-buffer: Have ring_buffer_iter_empty() return true when empty 2017-04-19 21:23:47 -04:00
.gitignore certs: add .gitignore to stop git nagging about x509_certificate_list 2015-10-21 15:18:35 +01:00
acct.c sched/headers: Prepare to move cputime functionality from <linux/sched.h> into <linux/sched/cputime.h> 2017-03-02 08:42:39 +01:00
async.c async: export current_is_async() 2015-11-19 17:51:48 +01:00
audit.c audit: make sure we don't let the retry queue grow without bounds 2017-04-10 11:16:59 -04:00
audit.h audit: move audit_signal_info() into kernel/auditsc.c 2017-03-27 14:30:06 -04:00
audit_fsnotify.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2016-12-17 18:44:00 -08:00
audit_tree.c Merge branch 'stable-4.10' of git://git.infradead.org/users/pcmoore/audit 2017-01-05 23:06:06 -08:00
audit_watch.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2016-12-17 18:44:00 -08:00
auditfilter.c audit: add support for session ID user filter 2016-11-29 15:10:12 -05:00
auditsc.c audit: move audit_signal_info() into kernel/auditsc.c 2017-03-27 14:30:06 -04:00
backtracetest.c
bounds.c
capability.c capability: export has_capability 2017-01-12 07:01:56 -07:00
compat.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
configs.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
context_tracking.c context_tracking: Switch to new static_branch API 2015-11-24 09:56:43 +01:00
cpu.c cpu/hotplug: Serialize callback invocations proper 2017-03-14 19:19:27 +01:00
cpu_pm.c kernel/cpu_pm: fix cpu_cluster_pm_exit comment 2015-09-03 02:42:20 +02:00
crash_dump.c
cred.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/coredump.h> 2017-03-02 08:42:28 +01:00
delayacct.c sched/headers: Prepare to move cputime functionality from <linux/sched.h> into <linux/sched/cputime.h> 2017-03-02 08:42:39 +01:00
dma.c
elfcore.c
exec_domain.c
exit.c userfaultfd: non-cooperative: rollback userfaultfd_exit 2017-03-09 17:01:09 -08:00
extable.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2017-02-22 10:15:09 -08:00
fork.c mm: Rename SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU 2017-04-18 11:42:36 -07:00
freezer.c freezer, oom: check TIF_MEMDIE on the correct task 2016-07-28 16:07:41 -07:00
futex.c futex: Add missing error handling to FUTEX_REQUEUE_PI 2017-03-14 21:45:36 +01:00
futex_compat.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
groups.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
hung_task.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/debug.h> 2017-03-02 08:42:34 +01:00
irq_work.c treewide: Remove old email address 2015-11-23 09:44:58 +01:00
jump_label.c This release has no new tracing features, just clean ups, minor fixes 2017-02-27 13:26:17 -08:00
kallsyms.c bpf: make jited programs visible in traces 2017-02-17 13:40:05 -05:00
kcmp.c ptrace: use fsuid, fsgid, effective creds for fs access checks 2016-01-20 17:09:18 -08:00
Kconfig.freezer
Kconfig.hz
Kconfig.locks locking/mutex: Allow MUTEX_SPIN_ON_OWNER when DEBUG_MUTEXES 2016-10-25 11:31:51 +02:00
Kconfig.preempt
kcov.c kcov: make kcov work properly with KASLR enabled 2016-12-20 09:48:47 -08:00
kexec.c kexec: allow architectures to override boot mapping 2016-08-02 19:35:27 -04:00
kexec_core.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk 2017-02-22 17:33:34 -08:00
kexec_file.c kexec, x86/purgatory: Unbreak it and clean it up 2017-03-10 20:55:09 +01:00
kexec_internal.h kexec, x86/purgatory: Unbreak it and clean it up 2017-03-10 20:55:09 +01:00
kmod.c sched/headers, vfs/execve: Prepare to move the do_execve*() prototypes from <linux/sched.h> to <linux/binfmts.h> 2017-03-02 08:42:39 +01:00
kprobes.c powerpc updates for 4.11 part 1. 2017-02-22 10:30:38 -08:00
ksysfs.c kernel/ksysfs.c: add __ro_after_init to bin_attribute structure 2017-02-24 17:46:56 -08:00
kthread.c cgroup, kthread: close race window where new kthreads can be migrated to non-root cgroups 2017-03-17 10:18:47 -04:00
latencytop.c sched/headers: Prepare to move sched_info_on() and force_schedstat_enabled() from <linux/sched.h> to <linux/sched/stat.h> 2017-03-02 08:42:39 +01:00
Makefile cgroup: move cgroup files under kernel/cgroup/ 2016-12-27 14:49:05 -05:00
membarrier.c Fix: Disable sys_membarrier when nohz_full is enabled 2017-01-23 11:32:16 -08:00
memremap.c mm: add private lock to serialize memory hotplug operations 2017-03-16 16:56:18 -07:00
module-internal.h
module.c Modules updates for v4.11 2017-02-22 17:08:33 -08:00
module_signing.c KEYS: Move the point of trust determination to __key_link() 2016-04-11 22:43:43 +01:00
notifier.c kernel/notifier.c: simplify expression 2017-02-24 17:46:56 -08:00
nsproxy.c cgroup: introduce cgroup namespaces 2016-02-16 13:04:58 -05:00
padata.c padata: avoid race in reordering 2017-03-24 21:51:33 +08:00
panic.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/debug.h> 2017-03-02 08:42:34 +01:00
params.c Nothing exciting, minor tweaks and cleanups. 2015-11-09 15:53:39 -08:00
pid.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task.h> 2017-03-02 08:42:35 +01:00
pid_namespace.c sched/headers: Prepare for the reduction of <linux/sched.h>'s signal API dependency 2017-03-02 08:42:37 +01:00
profile.c sched/headers: Prepare to move sched_info_on() and force_schedstat_enabled() from <linux/sched.h> to <linux/sched/stat.h> 2017-03-02 08:42:39 +01:00
ptrace.c ptrace: fix PTRACE_LISTEN race corrupting task->state 2017-04-08 00:47:48 -07:00
range.c
reboot.c kexec: split kexec_load syscall from kexec core code 2015-09-10 13:29:01 -07:00
relay.c lib/vsprintf.c: remove %Z support 2017-02-27 18:43:47 -08:00
resource.c /proc/iomem: only expose physical resource addresses to privileged users 2016-04-14 12:56:09 -07:00
seccomp.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task_stack.h> 2017-03-02 08:42:36 +01:00
signal.c mm: Rename SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU 2017-04-18 11:42:36 -07:00
smp.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/idle.h> 2017-03-02 08:42:26 +01:00
smpboot.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task.h> 2017-03-02 08:42:35 +01:00
smpboot.h cpu/hotplug: Create hotplug threads 2016-03-01 20:36:56 +01:00
softirq.c softirq: Display IRQ_POLL for irq-poll statistics 2016-10-21 15:45:47 -06:00
stacktrace.c stacktrace, lockdep: Fix address, newline ugliness 2017-02-08 08:21:31 +01:00
stop_machine.c locking/core, stop_machine: Yield the CPU during stop machine() 2016-11-16 10:15:09 +01:00
sys.c sched/headers: Prepare to move cputime functionality from <linux/sched.h> into <linux/sched/cputime.h> 2017-03-02 08:42:39 +01:00
sys_ni.c move aio compat to fs/aio.c 2016-12-22 22:58:37 -05:00
sysctl.c sysctl: report EINVAL if value is larger than UINT_MAX for proc_douintvec 2017-04-08 10:27:40 -07:00
sysctl_binary.c sysctl: add KERN_CONT to deprecated_sysctl_warning() 2016-12-14 16:04:07 -08:00
task_work.c task_work: use READ_ONCE/lockless_dereference, avoid pi_lock if !task_works 2016-08-02 19:35:02 -04:00
taskstats.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2016-11-15 10:54:36 -05:00
test_kprobes.c
torture.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/clock.h> 2017-03-02 08:42:27 +01:00
tracepoint.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task.h> 2017-03-02 08:42:35 +01:00
tsacct.c sched/headers: Prepare to move cputime functionality from <linux/sched.h> into <linux/sched/cputime.h> 2017-03-02 08:42:39 +01:00
ucount.c ucount: Remove the atomicity from ucount->count 2017-03-06 15:26:37 -06:00
uid16.c sched/headers: Prepare to remove <linux/cred.h> inclusion from <linux/sched.h> 2017-03-02 08:42:31 +01:00
up.c smp: Add function to execute a function synchronously on a CPU 2016-09-05 13:52:39 +02:00
user-return-notifier.c
user.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/user.h> 2017-03-02 08:42:29 +01:00
user_namespace.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/signal.h> 2017-03-02 08:42:29 +01:00
utsname.c sched/headers: Prepare to move the task_lock()/unlock() APIs to <linux/sched/task.h> 2017-03-02 08:42:38 +01:00
utsname_sysctl.c sched/headers: Remove <linux/rwsem.h> from <linux/sched.h> 2017-03-03 01:45:36 +01:00
watchdog.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/debug.h> 2017-03-02 08:42:34 +01:00
watchdog_hld.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/debug.h> 2017-03-02 08:42:34 +01:00
workqueue.c workqueue: trigger WARN if queue_delayed_work() is called with NULL @wq 2017-03-06 15:33:42 -05:00
workqueue_internal.h sched/core: Get rid of 'cpu' argument in wq_worker_sleeping() 2016-03-02 10:28:47 -05:00