linux-kernel - Re: [PATCH v2 5/6] sched/dl: Optimize select_task_rq

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Date:	Tue, 4 Nov 2014 16:11:09 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"pang.xunlei" <pang.xunlei@...aro.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@...il.com>
Subject: Re: [PATCH v2 5/6] sched/dl: Optimize select_task_rq_dl() for non-DL
 curr task

On Tue, Nov 04, 2014 at 09:45:49AM -0500, Steven Rostedt wrote:
> > +++ b/kernel/sched/deadline.c
> > @@ -954,6 +954,9 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags)
> >  	struct task_struct *curr;
> >  	struct rq *rq;
> >  
> > +	if (p->nr_cpus_allowed == 1)
> > +		goto out;
> > +
> 
> This looks fine, and I'm wondering if we shouldn't just move this into
> kernel/sched/core.c: select_task_rq(). Why bother calling the select_rq
> code if the task is pinned?
> 
> This change will make fair.c, rt.c, and deadline.c all start with the
> same logic. If this should be an optimization, just move it to core.c
> and be done with it.

Yeah, that makes sense. Back when, in the olden days, nr_cpus_allowed
was specific to the rt class, but we fixed that.
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