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cfq-iosched: remove limit of dispatch depth of max 4 times quantum

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This basically limits the hardware queue depth to 4*quantum at any
point in time, which is 16 with the default settings. As CFQ uses
other means to shrink the hardware queue when necessary in the first
place, there's really no need for this extra heuristic. Additionally,
it ends up hurting performance in some cases.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2008-10-20 15:44:28 +02:00
parent 31dcfab0ae
commit 30e0dc28bf
1 changed files with 2 additions and 6 deletions
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8
block/cfq-iosched.c
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@ -1136,12 +1136,8 @@ static int cfq_dispatch_requests(struct request_queue *q, int force)
if (cfq_class_idle(cfqq))
max_dispatch = 1;
if (cfqq->dispatched >= max_dispatch) {
if (cfqd->busy_queues > 1)
break;
if (cfqq->dispatched >= 4 * max_dispatch)
break;
}
if (cfqq->dispatched >= max_dispatch && cfqd->busy_queues > 1)
break;
if (cfqd->sync_flight && !cfq_cfqq_sync(cfqq))
break;