From: Oleg Nesterov <oleg@redhat.com>
Date: Wed, 23 Sep 2009 22:56:47 +0000 (-0700)
Subject: do_wait() wakeup optimization: child_wait_callback: check __WNOTHREAD case
X-Git-Tag: v2.6.32-rc1~109
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b4fe51823d797d6959b2eee7868023e61606daa9;p=pandora-kernel.git

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>
---

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