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authorOleg Nesterov <oleg@redhat.com>2009-09-23 15:56:47 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-09-24 07:21:00 -0700
commitb4fe51823d797d6959b2eee7868023e61606daa9 (patch)
treee078feaa1cdfbbdc98b5f5f668fecc37c1907b2e
parent0b7570e77f7c3abd43107dabc47ea89daf9a1cba (diff)
do_wait() wakeup optimization: child_wait_callback: check __WNOTHREAD case
Suggested by Roland. do_wait(__WNOTHREAD) can only succeed if the caller is either ptracer, or it is ->real_parent and the child is not traced. IOW, caller == p->parent otherwise we should not wake up. Change child_wait_callback() to check this. Ratan reports the workload with CPU load >99% caused by unnecessary wakeups, should be fixed by this patch. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Roland McGrath <roland@redhat.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Ratan Nalumasu <rnalumasu@gmail.com> Cc: Vitaly Mayatskikh <vmayatsk@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--kernel/exit.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index 7838b4d68774..270a68b7f22f 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1581,6 +1581,9 @@ static int child_wait_callback(wait_queue_t *wait, unsigned mode,
if (!eligible_child(wo, p))
return 0;
+ if ((wo->wo_flags & __WNOTHREAD) && wait->private != p->parent)
+ return 0;
+
return default_wake_function(wait, mode, sync, key);
}