From: Aaron Carroll <aaronc@gelato.unsw.edu.au>
Date: Tue, 26 Aug 2008 13:52:36 +0000 (+0200)
Subject: cfq-iosched: fix queue depth detection
X-Git-Tag: v2.6.28-rc1~733^2~71
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=45333d5a31296d0af886d94f1d08f128231cab8e;p=pandora-kernel.git

cfq-iosched: fix queue depth detection

CFQ's detection of queueing devices assumes a non-queuing device and detects
if the queue depth reaches a certain threshold.  Under some workloads (e.g.
synchronous reads), CFQ effectively forces a unit queue depth, thus defeating
the detection logic.  This leads to poor performance on queuing hardware,
since the idle window remains enabled.

This patch inverts the sense of the logic: assume a queuing-capable device,
and detect if the depth does not exceed the threshold.

Signed-off-by: Aaron Carroll <aaronc@gelato.unsw.edu.au>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
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