linux-kernel - Re: [RFC][PATCH] CPUSets: Move most calls to rebuild_sched

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Message-ID: <48647267.3030606@qualcomm.com>
Date:	Thu, 26 Jun 2008 21:53:59 -0700
From:	Max Krasnyansky <maxk@...lcomm.com>
To:	ego@...ibm.com
CC:	Paul Menage <menage@...gle.com>,
	Vegard Nossum <vegard.nossum@...il.com>,
	Paul Jackson <pj@....com>, a.p.zijlstra@...llo.nl,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...sign.ru>
Subject: Re: [RFC][PATCH] CPUSets: Move most calls to	rebuild_sched_domains()
 to the workqueue

Gautham R Shenoy wrote:
> On Fri, Jun 27, 2008 at 08:52:28AM +0530, Gautham R Shenoy wrote:
>> On Thu, Jun 26, 2008 at 12:56:49AM -0700, Paul Menage wrote:
>>> CPUsets: Move most calls to rebuild_sched_domains() to the workqueue
>>>
>>> In the current cpusets code the lock nesting between cgroup_mutex and
>>> cpuhotplug.lock when calling rebuild_sched_domains is inconsistent -
>>> in the CPU hotplug path cpuhotplug.lock nests outside cgroup_mutex,
>>> and in all other paths that call rebuild_sched_domains() it nests
>>> inside.
>>>
>>> This patch makes most calls to rebuild_sched_domains() asynchronous
>>> via the workqueue, which removes the nesting of the two locks in that
>>> case. In the case of an actual hotplug event, cpuhotplug.lock nests
>>> outside cgroup_mutex as now.
>>>
>> Using a multithreaded workqueue(kevent here) for this is not such a
>> great idea this,since currently we cannot call
>> get_online_cpus() from a workitem executed by a multithreaded workqueue.
>>
>> Can one use a single threaded workqueue here instead ?
We could certainly do it in the single threaded workqueue. It won't help to
avoid circular locking dependencies though.
Did you get a chance to read entire thread on this topic ? There were some
questions that you might be able to answer.

Max
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