linux-kernel - Re: [patch] Reorganize the cpufreq cpu hotplug locking to not be totally bizare

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Message-ID: <20060726155114.GA28945@redhat.com>
Date:	Wed, 26 Jul 2006 11:51:14 -0400
From:	Dave Jones <davej@...hat.com>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Linus Torvalds <torvalds@...l.org>, Ingo Molnar <mingo@...e.hu>,
	Chuck Ebbert <76306.1226@...puserve.com>,
	Ashok Raj <ashok.raj@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>
Subject: Re: [patch] Reorganize the cpufreq cpu hotplug locking to not be totally bizare

On Wed, Jul 26, 2006 at 03:40:07PM +0200, Arjan van de Ven wrote:

 > Subject: Reorganize the cpufreq cpu hotplug locking to not be totally bizare
 > From: Arjan van de Ven <arjan@...ux.intel.com>
 > 
 > The patch below moves the cpu hotplugging higher up in the cpufreq
 > layering; this is needed to avoid recursive taking of the cpu hotplug
 > lock and to otherwise detangle the mess.
 > 
 > The new rules are:
 > 1. you must do lock_cpu_hotplug() around the following functions:
 >    __cpufreq_driver_target
 >    __cpufreq_governor (for CPUFREQ_GOV_LIMITS operation only)
 >    __cpufreq_set_policy
 > 2. governer methods (.governer) must NOT take the lock_cpu_hotplug()
 >    lock in any way; they are called with the lock taken already
 > 3. if your governer spawns a thread that does things, like calling
 >    __cpufreq_driver_target, your thread must honor rule #1.
 > 4. the policy lock and other cpufreq internal locks nest within 
 >    the lock_cpu_hotplug() lock. 
 > 
 > I'm not entirely happy about how the __cpufreq_governor rule ended up
 > (conditional locking rule depending on the argument) but basically all
 > callers pass this as a constant so it's not too horrible.
 > 
 > The patch also removes the cpufreq_governor() function since during the
 > locking audit it turned out to be entirely unused (so no need to fix it)
 > 
 > The patch works on my testbox, but it could use more testing 
 > (otoh... it can't be much worse than the current code)
 > 
 > Signed-off-by: Arjan van de Ven <arjan@...ux.intel.com>

Looks sensible to me.   Assuming it passes testing..

Signed-off-by: Dave Jones <davej@...hat.com>

Linus ?

		Dave

-- 
http://www.codemonkey.org.uk
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