linux-kernel - Re: [PATCH] sched: remove redundant check in select_task_rq

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Message-ID: <1307441361.2322.239.camel@twins>
Date:	Tue, 07 Jun 2011 12:09:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>
Cc:	mingo@...e.hu, linux-kernel@...r.kernel.org,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>
Subject: Re: [PATCH] sched: remove redundant check in select_task_rq_fair

On Tue, 2011-06-07 at 15:34 +0530, Nikunj A. Dadhania wrote:
> On Tue, 07 Jun 2011 11:53:34 +0200, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Tue, 2011-06-07 at 15:18 +0530, Nikunj A. Dadhania wrote:
> > > When balancing for wakeup affinity, a redundant check can removed.
> > 
> > Yes, tempting, but no, now you've got an extra call to wake_affine(),
> > which is more expensive.

> Ah, got that. How about this, it is more readable. Other options would
> be to add a comment.

> -		if (cpu == prev_cpu || wake_affine(affine_sd, p, sync))
> +		if (cpu != prev_cpu && wake_affine(affine_sd, p, sync))
>  			prev_cpu = cpu;

I guess that depends on which way your head is wired and how strong your
boolean algebra is.. Suresh, Mike any preference? I don't much care
either way.
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