linux-kernel - Re: [PATCH 4/7] sched: implement force_cpus

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Message-ID: <4B1E189B.1070204@kernel.org>
Date:	Tue, 08 Dec 2009 18:12:59 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	tglx@...utronix.de, mingo@...e.hu, avi@...hat.com, efault@....de,
	rusty@...tcorp.com.au, linux-kernel@...r.kernel.org,
	Gautham R Shenoy <ego@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 4/7] sched: implement force_cpus_allowed()

Hello,

On 12/08/2009 06:02 PM, Peter Zijlstra wrote:
> So its only needed in order to flush a workqueue from CPU_DOWN_PREPARE?
> And all you need it to place a new kthread on a !active cpu?

Yes, that's all I need.

> Or is this in order to allow migrate_live_tasks() to move the worker
> threads away from the dead cpu?

Nope, that's left to sched cpu callbacks.

> I'm really not thrilled by the whole fork-fest workqueue design.

Shared work pool kind of needs forks unless it's gonna create all the
workers upfront.  Most issues arise from corner cases - deadlocks, cpu
hotplugging, freeze/thaw and so on.  During usual operation, the
thread pool would remain largely stable.

Thanks.

-- 
tejun
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