Message-ID: <1373781316.7242.34.camel@marge.simpson.net>
Subject: Re: [PATCH] sched: Add logic to handle parallel try_to_wake_up() of
 the same task
From: Mike Galbraith <bitbucket@online.de>
To: Kirill Tkhai <tkhai@yandex.ru>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>
Date: Sun, 14 Jul 2013 07:55:16 +0200
In-Reply-To: <1517081373730349@web23d.yandex.ru>
References: <1517081373730349@web23d.yandex.ru>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Mime-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1241
Lines: 28

On Sat, 2013-07-13 at 19:45 +0400, Kirill Tkhai wrote: 
> This patch adds optimization of try_to_wake_up() function
> for cases when the system is doing parallel wake_up
> of the same task on the different cpus. Also it adds
> accounting the statistics of these situations.
> 
> We check the status of the task we want to wake up.
> If it is TASK_WAKING then the task is manipulated
> by try_to_wake_up() on another cpu. And after this
> check it will be a moment when the task is queued
> and his status is TASK_RUNNING. We just return
> earlier when we are sure the task will be TASK_RUNNING
> in the future (maybe right after the check). The profit is
> we don't loop while we are waiting the spinlock.

Hm, you're adding cycles to the common case to shave spin cycles in the
very rare case, then spending some to note that a collision happened.
What makes recording worth even 1 cycle?  What am I gonna do with the
knowledge that $dinkynum wakeups intersected at a some random task?

-Mike


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/