linux-kernel - Re: [RFC][PATCH 2/2] add a counter for writers spinning on a rwlock

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Date:	Mon, 26 Jan 2009 14:48:35 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mandeep Singh Baines <msb@...gle.com>
Subject: Re: [RFC][PATCH 2/2] add a counter for writers spinning on a rwlock

On Sun, 2009-01-25 at 12:50 -0800, Frederic Weisbecker wrote:
> This patch adds a counter for writers that enter a rwlock slow path.
> For example it can be useful for slow background tasks which perform some jobs
> on the tasklist, such as the hung_task detector (kernel/hung_task.c).
> 
> It adds a inc/dec pair on the slow path and 4 bytes for each rwlocks, so the overhead
> is not null.
> 
> Only x86 is supported for now, writers_spinning_lock() will return 0 on other archs (which
> is perhaps not a good idea).
> 
> Comments?

_why_ ?



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