linux-kernel - Re: [PATCH 6/6] x86 rwsem: more precise rwsem_is

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Message-ID: <1291416070.2032.92.camel@laptop>
Date:	Fri, 03 Dec 2010 23:41:10 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Nick Piggin <npiggin@...nel.dk>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 6/6] x86 rwsem: more precise rwsem_is_contended()
 implementation

On Thu, 2010-12-02 at 16:16 -0800, Michel Lespinasse wrote:
> We would like rwsem_is_contended() to return true only once a contending
> writer has had a chance to insert itself onto the rwsem wait queue.
> To that end, we need to differenciate between active and queued writers.

So you're only considering writer-writer contention? Not writer-reader
and reader-writer contention?

I'd argue rwsem_is_contended() should return true if there is _any_
blocked task, be it a read or a writer.

If you want something else call it something else, like
rwsem_is_write_contended() (there's a pending writer), or
rwsem_is_read_contended() (there's a pending reader).


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