linux-kernel - Re: [PATCH] sched: remove resetting exec_start in put_prev_task

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Date:	Thu, 09 Jun 2011 08:34:23 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Yong Zhang <yong.zhang0@...il.com>
Cc:	Hillf Danton <dhillf@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] sched: remove resetting exec_start in
 put_prev_task_rt()

On Thu, 2011-06-02 at 16:04 +0800, Yong Zhang wrote:
> On Wed, Jun 1, 2011 at 10:03 PM, Hillf Danton <dhillf@...il.com> wrote:
> > Resetting exec_start, after updated in update_curr_rt(), could open window for
> > messing up the subsequent computations of delta_exec of the given task.
> 
> I can't see how could this happen. what kind of 'subsequent computations'
> do you mean?

I still don't see a race.

Hilf, if you still believe there's a race here, can you explain it in
detail. Do something like:

	CPU0			CPU1
	----			----
   do_something;
				does_something_not_expected;
   continue_something;

Obviously changing what those "somethings" are. That way we can visually
see what you are trying to say.

> 
> But because exec_start will be reset by _pick_next_task_rt()/set_curr_task_rt(),
> you patch is ok. IMHO it is not critical, it's just cleanup instead.

I disagree. Yes the exec_start is reset there, but I like the fact that
it's 0 when not running.

-- Steve


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