linux-kernel - Re: [PATCH 00/11] V4: rwsem changes + down_read

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Date:	Thu, 27 May 2010 04:47:56 -0700
From:	Michel Lespinasse <walken@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	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 00/11] V4: rwsem changes + down_read_critical() proposal

On Thu, May 27, 2010 at 4:18 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, 2010-05-27 at 03:59 -0700, Michel Lespinasse wrote:
>> What about patches 1-7 which don't deal with the critical/atomic API;
>> can we agree to get these in before we we figure out what to do with
>> the the last 4 ?
>
> patch 6 looks like it will break fairness, either that or the changelog
> got me totally confused (already had to read it twice).

Hmmm. I must be bad at explaining this :)

It avoids a situation where threads got blocked waiting for all active
readers to release, but (due to a race condition when blocking) the
first queued thread is also a reader. Letting that reader proceed in
parallel with the currently active ones will not delay queued writers;
they would have had to wait for the first queued reader to proceed
anyway since they were queued behind it.

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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