linux-kernel - Re: [BUG 2.6.25-rc3] scheduler/hotplug: some processes are dealocked when cpu is set to offline

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Message-ID: <20080307135537.GB10576@in.ibm.com>
Date:	Fri, 7 Mar 2008 19:25:37 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	Dmitry Adamushko <dmitry.adamushko@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Oleg Nesterov <oleg@...sign.ru>,
	Yi Yang <yi.y.yang@...el.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [BUG 2.6.25-rc3] scheduler/hotplug: some processes are
	dealocked when cpu is set to offline

On Fri, Mar 07, 2008 at 02:02:20PM +0100, Dmitry Adamushko wrote:
> Hi,
> 
> 'watchdog' is of SCHED_FIFO class. The standard load-balancer doesn't
> move RT tasks between cpus anymore and there is a special mechanism in
> scher_rt.c instead (I think, it's .25 material).
> 
> So I wonder, whether __migrate_task() is still capable of properly
> moving a RT task to another CPU (e.g. for the case when it's in
> TASK_RUNNING state) without breaking something in the rt migration
> mechanism (or whatever else) that would leave us with a runqueue in
> the 'inconsistent' state...
> (I've taken a quick look at the relevant code so can't confirm it yet)
> 
> maybe it'd be faster if somebody could do a quick test now with the
> following line commented out in kernel/softlockup.c :: watchdog()
> 
> -         sched_setscheduler(current, SCHED_FIFO, &param);

Commenting out that like seems to work. Passed 500 iterations of
cpu-hotplug without any problems.

> 
> 
> -- 
> Best regards,
> Dmitry Adamushko

-- 
Thanks and Regards
gautham
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