linux-kernel - Re: SCHED: Is task migration necessary in sched

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Message-ID: <b9df5fa10912230335r459f86d4te868fca82b891752@mail.gmail.com>
Date:	Wed, 23 Dec 2009 17:35:48 +0600
From:	Rakib Mullick <rakib.mullick@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: SCHED: Is task migration necessary in sched_exec().

On 12/23/09, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, 2009-12-23 at 16:46 +0600, Rakib Mullick wrote:
>  > On 12/23/09, Peter Zijlstra <peterz@...radead.org> wrote:
>  > > On Wed, 2009-12-23 at 16:14 +0600, Rakib Mullick wrote:
>
> There is no overloaded task, its the runqueue that is overloaded wrt to
>  other runqueues. The load-balancer has to pick a 'random' task and pray.

By saying overloaded task - I didn't want to mean any perticular task.
I wanted to mean a runqueue of excessive tasks with regard to other
runqueue (sorry for misleading you).

>  Current heuristics try to pick a task that hasn't been on the cpu for a
>  while, because for those the effective cache footprint is minimal.
>
Yes - current heuristics does this - to make sure that it doesn't have to
wait too long. It pushes process into another runqueue (probably less loaded)
just to make sure that - it will get the CPU a bit quickly. But when a task
got the CPU - we should keep it out of equation. The point of moving task
is - it have to wait less. At exec current task don't have to wait to get CPU.

>  > Why the _current_ task?
>
>  Because at exec it has effective 0 cache footprint, and is thus an ideal
>  victim to move about.
>
>
>
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