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cfq-iosched: fix sequential write regression 

We have a 10-15% performance regression for sequential writes on TCQ/NCQ
enabled drives in 2.6.21-rcX after the CFQ update went in.  It has been
reported by Valerie Clement <valerie.clement@bull.net> and the Intel
testing folks.  The regression is because of CFQ's now more aggressive
queue control, limiting the depth available to the device.

This patches fixes that regression by allowing a greater depth when only
one queue is busy.  It has been tested to not impact sync-vs-async
workloads too much - we still do a lot better than 2.6.20.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jens Axboe 2007-04-20 08:55:52 +02:00 committed by Linus Torvalds
parent 46fcc86dd7
commit a993800655
1 changed files with 19 additions and 15 deletions
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34
block/cfq-iosched.c
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@ -986,9 +986,9 @@ __cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
* expire an async queue immediately if it has used up its slice. idle
* queue always expire after 1 dispatch round.
*/
if ((!cfq_cfqq_sync(cfqq) &&
if (cfqd->busy_queues > 1 && ((!cfq_cfqq_sync(cfqq) &&
cfqd->dispatch_slice >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
cfq_class_idle(cfqq)) {
cfq_class_idle(cfqq))) {
cfqq->slice_end = jiffies + 1;
cfq_slice_expired(cfqd, 0, 0);
}
@ -1051,19 +1051,21 @@ cfq_dispatch_requests(request_queue_t *q, int force)
while ((cfqq = cfq_select_queue(cfqd)) != NULL) {
int max_dispatch;
/*
* Don't repeat dispatch from the previous queue.
*/
if (prev_cfqq == cfqq)
break;
if (cfqd->busy_queues > 1) {
/*
* Don't repeat dispatch from the previous queue.
*/
if (prev_cfqq == cfqq)
break;
/*
* So we have dispatched before in this round, if the
* next queue has idling enabled (must be sync), don't
* allow it service until the previous have continued.
*/
if (cfqd->rq_in_driver && cfq_cfqq_idle_window(cfqq))
break;
/*
* So we have dispatched before in this round, if the
* next queue has idling enabled (must be sync), don't
* allow it service until the previous have continued.
*/
if (cfqd->rq_in_driver && cfq_cfqq_idle_window(cfqq))
break;
}
cfq_clear_cfqq_must_dispatch(cfqq);
cfq_clear_cfqq_wait_request(cfqq);
@ -1370,7 +1372,9 @@ retry:
atomic_set(&cfqq->ref, 0);
cfqq->cfqd = cfqd;
cfq_mark_cfqq_idle_window(cfqq);
if (key != CFQ_KEY_ASYNC)
cfq_mark_cfqq_idle_window(cfqq);
cfq_mark_cfqq_prio_changed(cfqq);
cfq_mark_cfqq_queue_new(cfqq);
cfq_init_prio_data(cfqq);