linux-kernel - Re: [RFC][PATCH 6/7] sched: Balance RT tasks when forked as well

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Message-ID: <1311684607.3526.67.camel@gandalf.stny.rr.com>
Date:	Tue, 26 Jul 2011 08:50:07 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH 6/7] sched: Balance RT tasks when forked as well

On Tue, 2011-07-26 at 14:36 +0200, Peter Zijlstra wrote:
> On Tue, 2011-07-26 at 08:35 -0400, Steven Rostedt wrote:
> > On Tue, 2011-07-26 at 14:25 +0200, Peter Zijlstra wrote:
> > > On Thu, 2011-06-16 at 21:55 -0400, Steven Rostedt wrote:
> > > > +       /* For anything but wake ups, just return the task_cpu */
> > > > +       if (sd_flag != SD_BALANCE_WAKE || sd_flag != SD_BALANCE_FORK) 
> > > 
> > > So we call select_task_rq() with SD_BALANCE_{WAKE,EXEC,FORK}, 
> > > 
> > > 	(WAKE != WAKE -> 0 || WAKE != FORK -> 1) -> 1
> > > 	(EXEC != WAKE -> 1 ) -> 1
> > > 	(FORK != WAKE -> 1 ) -> 1
> > > 
> > > IOW, you never end up doing anything now.. surely you didn't mean that?!
> > 
> > Bah!
> > 
> > s/||/&&/
> 
> So you only want to rebalance on EXEC? The comment says you want to
> balance on wakeups. Please as to unconfuse!?

The patch is (with fixup):

+       /* For anything but wake ups, just return the task_cpu */
+       if (sd_flag != SD_BALANCE_WAKE && sd_flag != SD_BALANCE_FORK)
+               goto out;

In other words, if it isn't a WAKE or FORK (FORK being new task wakeup)
then exit the routine.

EXEC should not rebalance.

-- Steve


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