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authorWaiman Long <Waiman.Long@hpe.com>2016-12-14 15:04:10 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-05-22 16:57:57 +0200
commit20a30619b3315c1f11565cfbc0dbe2ea92a8a003 (patch)
treeab1f10a155003c34b1a44096fe7d7e8e4b093390 /include
parent0c8b8d37c85805ebc47a3e6a5f799bad4de8328e (diff)
signals: avoid unnecessary taking of sighand->siglock
commit c7be96af89d4b53211862d8599b2430e8900ed92 upstream. 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> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/signal.h17
1 files changed, 17 insertions, 0 deletions
diff --git a/include/linux/signal.h b/include/linux/signal.h
index b63f63eaa39c..5308304993be 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