linux-kernel - Re: [PATCH v4 1/2] workqueue: add new schedule_on_cpu

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Message-ID: <20130809150257.GM20515@mtj.dyndns.org>
Date:	Fri, 9 Aug 2013 11:02:57 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Chris Metcalf <cmetcalf@...era.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Cody P Schafer <cody@...ux.vnet.ibm.com>
Subject: Re: [PATCH v4 1/2] workqueue: add new schedule_on_cpu_mask() API

Hello, Chris.

On Wed, Aug 07, 2013 at 04:49:44PM -0400, Chris Metcalf wrote:
> This primitive allows scheduling work to run on a particular set of
> cpus described by a "struct cpumask".  This can be useful, for example,
> if you have a per-cpu variable that requires code execution only if the
> per-cpu variable has a certain value (for example, is a non-empty list).

So, this allows scheduling work items on !online CPUs.  Workqueue does
allow scheduling per-cpu work items on offline CPUs if the CPU has
ever been online, but the behavior when scheduling work items on cpu
which has never been online is undefined.  I think the interface at
least needs to verify that the the target cpus have been online,
trigger warning and mask off invalid CPUs otherwise.

Thanks.

-- 
tejun
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