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authorWaiman Long <Waiman.Long@hpe.com>2016-12-14 15:04:10 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-12-14 16:04:07 -0800
commitc7be96af89d4b53211862d8599b2430e8900ed92 (patch)
tree91754f99fd7f1ac925433b5aa833b747bcfb312e /kernel/signal.c
parent73e64c51afc56d4863ae225e947ba2f16ad04487 (diff)
downloadlinux-c7be96af89d4b53211862d8599b2430e8900ed92.tar.bz2
signals: avoid unnecessary taking of sighand->siglock
When running certain database workload on a high-end system with many CPUs, it was found that spinlock contention in the sigprocmask syscalls became a significant portion of the overall CPU cycles as shown below. 9.30% 9.30% 905387 dataserver /proc/kcore 0x7fff8163f4d2 [k] _raw_spin_lock_irq | ---_raw_spin_lock_irq | |--99.34%-- __set_current_blocked | sigprocmask | sys_rt_sigprocmask | system_call_fastpath | | | |--50.63%-- __swapcontext | | | | | |--99.91%-- upsleepgeneric | | | |--49.36%-- __setcontext | | ktskRun Looking further into the swapcontext function in glibc, it was found that the function always call sigprocmask() without checking if there are changes in the signal mask. A check was added to the __set_current_blocked() function to avoid taking the sighand->siglock spinlock if there is no change in the signal mask. This will prevent unneeded spinlock contention when many threads are trying to call sigprocmask(). With this patch applied, the spinlock contention in sigprocmask() was gone. Link: http://lkml.kernel.org/r/1474979209-11867-1-git-send-email-Waiman.Long@hpe.com Signed-off-by: Waiman Long <Waiman.Long@hpe.com> Acked-by: Oleg Nesterov <oleg@redhat.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Stas Sergeev <stsp@list.ru> Cc: Scott J Norton <scott.norton@hpe.com> Cc: Douglas Hatch <doug.hatch@hpe.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/signal.c')
-rw-r--r--kernel/signal.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/kernel/signal.c b/kernel/signal.c
index 29a410780aa9..ae60996fedff 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2491,6 +2491,13 @@ void __set_current_blocked(const sigset_t *newset)
{
struct task_struct *tsk = current;
+ /*
+ * In case the signal mask hasn't changed, there is nothing we need
+ * to do. The current->blocked shouldn't be modified by other task.
+ */
+ if (sigequalsets(&tsk->blocked, newset))
+ return;
+
spin_lock_irq(&tsk->sighand->siglock);
__set_task_blocked(tsk, newset);
spin_unlock_irq(&tsk->sighand->siglock);