linux-kernel - Re: [PATCH][RFC] kernel/cpu: do not change the cpus_allowed of the current task when unplugging cpus

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Date:	Mon, 17 Jun 2013 13:49:46 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Zhao Chenhui <chenhui.zhao@...escale.com>
CC:	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, leoli@...escale.com, scottwood@...escale.com,
	Priyanka.Jain@...escale.com
Subject: Re: [PATCH][RFC] kernel/cpu: do not change the cpus_allowed of the
 current task when unplugging cpus

On 06/17/2013 12:48 PM, Zhao Chenhui wrote:
> I don't think it is necessary to change the mask. migration_call() invoked by
> the cpu notify "CPU_DYING" will remove all running tasks from the dying cpu.
> Even if the current task is running on the dying cpu, it will be transfered
> to another online cpu. 

I had here hiccups if the task was running on the CPU which should go
down.

> I guess that changing the mask benefits the latency of the system.
> Please correct me.

I don't get this. Lets say your system has CPUs 0-15 and you pin your
application to CPU0. After this application brings CPU15 down it is
allowed to run on CPUs 0-14. This is wrong and has been corrected. The
CPU down mechanism should not affected CPU mask of the application.

> 
> -Chenhui
> 

Sebastian
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