linux-kernel - Re: [PATCH 06/12] rwsem: wake queued readers when other readers are active

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Message-ID: <22741.1273666943@redhat.com>
Date:	Wed, 12 May 2010 13:22:23 +0100
From:	David Howells <dhowells@...hat.com>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	dhowells@...hat.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Waychison <mikew@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH 06/12] rwsem: wake queued readers when other readers are active

Michel Lespinasse <walken@...gle.com> wrote:

> In this situation, it would be perfectly fine to let threads B and C work
> in parallel as they each only want a read acquire on the rwsem. We can
> recognize this situation and let A wake B as long as there are no active
> writers on the rwsem.

There can't be any active writers on the rwsem.  An active writer must have
just been upped and is in the process of waking the first sleeper up.

David
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