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/[email protected]
Signed-off-by: Waiman Long <[email protected]>
Acked-by: Oleg Nesterov <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Stas Sergeev <[email protected]>
Cc: Scott J Norton <[email protected]>
Cc: Douglas Hatch <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
diff --git a/include/linux/signal.h b/include/linux/signal.h
index b63f63e..5308304 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -97,6 +97,23 @@ static inline int sigisemptyset(sigset_t *set)
}
}
+static inline int sigequalsets(const sigset_t *set1, const sigset_t *set2)
+{
+ switch (_NSIG_WORDS) {
+ case 4:
+ return (set1->sig[3] == set2->sig[3]) &&
+ (set1->sig[2] == set2->sig[2]) &&
+ (set1->sig[1] == set2->sig[1]) &&
+ (set1->sig[0] == set2->sig[0]);
+ case 2:
+ return (set1->sig[1] == set2->sig[1]) &&
+ (set1->sig[0] == set2->sig[0]);
+ case 1:
+ return set1->sig[0] == set2->sig[0];
+ }
+ return 0;
+}
+
#define sigmask(sig) (1UL << ((sig) - 1))
#ifndef __HAVE_ARCH_SIG_SETOPS
