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

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Message-ID: <1260272885.3935.1189.camel@laptop>
Date:	Tue, 08 Dec 2009 12:48:05 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tejun Heo <tj@...nel.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()

On Tue, 2009-12-08 at 20:24 +0900, Tejun Heo wrote:
> 
> Let me augment the above sentence.  Yes, that's all I need *during
> CPU_DOWN*.  During CPU_UP, I need to migrate back left running workers
> which survived from the last CPU_DOWN.  In the original patch, the
> down path is worker_maybe_bind_and_lock() and the latter path is
> trustee_unset_rogue(). 

Why bother with that?

workqueue's CPU_POST_DEAD will flush the workqueue and destroy all
threads under cpu_add_remove_lock, which excludes the cpu from coming
back up before its fully destroyed.

So there's no remaining tasks to be migrated back.

Changing that semantics is not worthwhile.

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