linux-kernel - Re: [RFC PATCH] sched: rt: fix selecting runqueue for task to be pushed

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Message-ID: <CAJd=RBDprA5ruzY6-uQ3L5eSX3Muk8fSpQZbbmsK0oAGwk0WtQ@mail.gmail.com>
Date:	Tue, 11 Dec 2012 20:10:09 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] sched: rt: fix selecting runqueue for task to be pushed

On Mon, Dec 10, 2012 at 10:21 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Mon, 2012-12-10 at 20:19 +0800, Hillf Danton wrote:
>> When we are trying to push task out, no point to select the last cpu that
>> the given task executed on, which is fixed by selecting target cpu with
>> cache affinity concerned, and with SD_WAKE_AFFINE ignored as we are not
>> handling sleeper.
>
> I have to ask. Why?
>
> The check you are skipping is if the task is running on a CPU that is
> already the lowest CPU priority (lowest_mask returns the CPUs running
> tasks of the lowest priority in the system).

Hm ... how do you get the lowest mask for a pushable task iff
that check makes sense?

> Which means that either the
> task that we are pushing is the same priority or lesser priority than
> what is running on the other CPUs. Either case, this task wont push out
> a task on the other CPUs because it's not higher priority than those
> tasks.
>
> You just added more work for the same result (no push).
>
> -- Steve
>
>
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