linux-kernel - Re: [PATCH RFC] pm_qos

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Message-ID: <alpine.DEB.1.10.0808291028540.27078@gandalf.stny.rr.com>
Date:	Fri, 29 Aug 2008 10:29:40 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	John Kacur <jkacur@...il.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>, mgross@...ux.intel.com,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	peterz@...radead.org, mingo@...e.hu, tglx@...utronix.de,
	arjan@...radead.org
Subject: Re: [PATCH RFC] pm_qos_requirement might sleep



On Fri, 29 Aug 2008, John Kacur wrote:
> 
> Hi Andrew
> 
> The purpose of the patch is to remove the spin_lock around the read in
> the function pm_qos_requirement - since spinlocks can sleep in -rt and
> this function is called from idle. I did propose a patch, that simply
> removed the spinlock, since Peter Zilstra and others (yourself) point
> out, the lock isn't needed to read a single word from memory. Although
> the patch worked fine, Arjan objected to it, because it was not
> symmetric. A reader of the code might wonder why it was locked in
> other functions but not here. He suggested changing it to an atomic
> type might be less confusing. The alternative which I like better
> actually is to simply remove the lock in pm_qos_requirement and add a
> comment for readers of the code.

This is a much better changelog, and is what should have been written in 
the first place ;-)

-- Steve

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