tree ea5b1afb70fb17935128bac6df588e6b5ae764b4
parent 605401618ce4409045bc4db86e88d4b38f2ad585
author Aaron Carroll <aaronc@gelato.unsw.edu.au> 1219758756 +0200
committer Jens Axboe <jens.axboe@oracle.com> 1223535369 +0200

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>