linux-kernel - Re: [PATCH 1/2] sched: Rework migrate

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Message-ID: <20140611105733.GM6758@twins.programming.kicks-ass.net>
Date:	Wed, 11 Jun 2014 12:57:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Kirill Tkhai <ktkhai@...allels.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	tkhai@...dex.ru
Subject: Re: [PATCH 1/2] sched: Rework migrate_tasks()

On Wed, Jun 11, 2014 at 01:52:10PM +0400, Kirill Tkhai wrote:
> 
> Currently migrate_tasks() skips throttled tasks,
> because they are not pickable by pick_next_task().
> 
> These tasks stay on dead cpu even after they
> becomes unthrottled. They are not schedulable
> till user manually changes their affinity or till
> cpu becomes alive again.
> 
> But for user this looks completely untransparent:
> task hangs, but it's not obvious what he has to do,
> because kernel does not report any problem.
> 
> This situation may easily be triggered intentionally.
> Playing with extremely small cpu.cfs_quota_us causes
> it almost in 100% cases. In usual life it's very rare,
> but still possible for some unhappy user.
> 

How about fixing the unthrottle code to validate the affinity?

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