From b4fe51823d797d6959b2eee7868023e61606daa9 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Wed, 23 Sep 2009 15:56:47 -0700 Subject: [PATCH] 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 Acked-by: Roland McGrath Cc: Ingo Molnar Cc: Ratan Nalumasu Cc: Vitaly Mayatskikh Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/exit.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/exit.c b/kernel/exit.c index 7838b4d..270a68b 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); } -- 2.7.4