linux-kernel - [PATCH v2 3/7] signal: retarget_shared_pending: optimize while_each

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Date:	Mon, 18 Apr 2011 15:45:18 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Nikita V. Youshchenko" <nyoushchenko@...sta.com>,
	Matt Fleming <matt@...sole-pimps.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 3/7] signal: retarget_shared_pending: optimize
	while_each_thread() loop

retarget_shared_pending() blindly does recalc_sigpending_and_wake() for
every sub-thread, this is suboptimal. We can check t->blocked and stop
looping once every bit in shared_pending has the new target.

Note: we do not take task_is_stopped_or_traced(t) into account, we are
not trying to speed up the signal delivery or to avoid the unnecessary
(but harmless) signal_wake_up(0) in this unlikely case.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---

 kernel/signal.c |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

--- sigprocmask/kernel/signal.c~3_optimize_retarget_loop	2011-04-17 21:08:05.000000000 +0200
+++ sigprocmask/kernel/signal.c	2011-04-17 21:28:21.000000000 +0200
@@ -2033,8 +2033,18 @@ static void retarget_shared_pending(stru
 
 	t = tsk;
 	while_each_thread(tsk, t) {
-		if (!signal_pending(t) && !(t->flags & PF_EXITING))
-			recalc_sigpending_and_wake(t);
+		if ((t->flags & PF_EXITING))
+			continue;
+		if (!has_pending_signals(&shared_pending, &t->blocked))
+			continue;
+
+		sigandsets(&shared_pending, &shared_pending, &t->blocked);
+
+		if (!signal_pending(t))
+			signal_wake_up(t, 0);
+
+		if (sigisemptyset(&shared_pending))
+			break;
 	}
 }
 

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