linux-kernel - Re: [PATCH] block: fix request sorting at unplug

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Message-ID: <4D98F061.5030003@kernel.dk>
Date:	Mon, 04 Apr 2011 00:10:41 +0200
From:	Jens Axboe <axboe@...nel.dk>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: fix request sorting at unplug

On 2011-04-02 17:37, Konstantin Khlebnikov wrote:
> Comparison function for list_sort() must be anticommutative,
> otherwise it is not sorting in ordinary meaning.
> 
> But fortunately list_sort() always check ((*cmp)(priv, a, b) <= 0)
> it not distinguish negative and zero, so comparison function can
> implement only less-or-equal instead of full three-way comparison.

Thanks, good catch! It's an optimization, so no breakage. But if you end
up often having > 1 queue plugged, it's a good optimization.

-- 
Jens Axboe

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