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>
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1 changed files with 19 additions and 15 deletions
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@ -986,9 +986,9 @@ __cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
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* expire an async queue immediately if it has used up its slice. idle
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* queue always expire after 1 dispatch round.
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*/
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if ((!cfq_cfqq_sync(cfqq) &&
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if (cfqd->busy_queues > 1 && ((!cfq_cfqq_sync(cfqq) &&
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cfqd->dispatch_slice >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
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cfq_class_idle(cfqq)) {
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cfq_class_idle(cfqq))) {
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cfqq->slice_end = jiffies + 1;
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cfq_slice_expired(cfqd, 0, 0);
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}
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@ -1051,19 +1051,21 @@ cfq_dispatch_requests(request_queue_t *q, int force)
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while ((cfqq = cfq_select_queue(cfqd)) != NULL) {
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int max_dispatch;
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/*
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* Don't repeat dispatch from the previous queue.
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*/
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if (prev_cfqq == cfqq)
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break;
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if (cfqd->busy_queues > 1) {
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/*
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* Don't repeat dispatch from the previous queue.
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*/
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if (prev_cfqq == cfqq)
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break;
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/*
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* So we have dispatched before in this round, if the
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* next queue has idling enabled (must be sync), don't
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* allow it service until the previous have continued.
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*/
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if (cfqd->rq_in_driver && cfq_cfqq_idle_window(cfqq))
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break;
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/*
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* So we have dispatched before in this round, if the
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* next queue has idling enabled (must be sync), don't
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* allow it service until the previous have continued.
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*/
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if (cfqd->rq_in_driver && cfq_cfqq_idle_window(cfqq))
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break;
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}
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cfq_clear_cfqq_must_dispatch(cfqq);
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cfq_clear_cfqq_wait_request(cfqq);
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@ -1370,7 +1372,9 @@ cfq_get_queue(struct cfq_data *cfqd, unsigned int key, struct task_struct *tsk,
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atomic_set(&cfqq->ref, 0);
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cfqq->cfqd = cfqd;
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cfq_mark_cfqq_idle_window(cfqq);
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if (key != CFQ_KEY_ASYNC)
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cfq_mark_cfqq_idle_window(cfqq);
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cfq_mark_cfqq_prio_changed(cfqq);
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cfq_mark_cfqq_queue_new(cfqq);
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cfq_init_prio_data(cfqq);
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