linux-kernel - Re: [PATCH v2 2/6] sched/rt: Optimize select_task_rq

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Message-ID: <CADcy93XK9-p3iFw28qeA=q9Fp4_Qbd1Hoig6Tu5G+QfwxNWiow@mail.gmail.com>
Date:	Tue, 4 Nov 2014 22:29:24 +0800
From:	"pang.xunlei" <pang.xunlei@...aro.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...il.com>
Subject: Re: [PATCH v2 2/6] sched/rt: Optimize select_task_rq_rt() for non-RT
 curr task

On 4 November 2014 20:52, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Tue,  4 Nov 2014 19:13:01 +0800
> "pang.xunlei" <pang.xunlei@...aro.org> wrote:
>
>> When selecting the cpu for a waking RT task, if curr is a non-RT
>> task which is bound only on this cpu, then we can give it a chance
>> to select a different cpu(definitely an idle cpu if existing) for
>> the RT task to avoid curr starving.
>
> Absolutely not! An RT task doesn't give a crap if a non RT task is
> bound to a CPU or not. We are not going to migrate an RT task to be
> nice to a bounded non-RT task.
>
> Migration is not cheap. It causes cache misses and TLB flushes. This is
> not something that should be taken lightly.
Ok, thanks!
But I think the PUSH operation optimized by the former patch is reasonable,
since PUSH itselft does involve the Migration. Do I miss something?

>
> Nack
>
> -- Steve
>
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