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

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Message-ID: <20060726212102.GA23787@in.ibm.com>
Date:	Wed, 26 Jul 2006 14:21:02 -0700
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Linus Torvalds <torvalds@...l.org>, Dave Jones <davej@...hat.com>,
	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 11:03:06PM +0200, Arjan van de Ven wrote:
> rwsems unfortunately help you zilch; an rwsem is just a mutex with a
> performance tweak, but from the deadlock perspective it's really a
> mutex.

ah ..didnt realize that. 

> I'm really starting to feel that the hotplug lock would have been better
> of being a refcount (with a waitqueue for zero) than a lock. While
> "refcount+waitqueue" sort of IS a lock, the semantics make more sense
> imo...

I think that will work, although you now need to deal with a global or per-cpu 
refcount now. Later is more cache-friendly, but dont think we have ready 
refcounting APIs for that?

-- 
Regards,
vatsa
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