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cfq-iosched: avoid probable slice overrun when idling 

If the average think time is larger than the remaining time slice
for any given queue, don't allow it to idle. A succesful idle also
means that we need to dispatch and complete a request, so if we don't
even have time left for the idle process, we would overrun the slice
in any case.

Signed-off-by: Corrado Zoccolo <czoccolo@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Corrado Zoccolo 2009-10-08 08:43:32 +02:00 committed by Jens Axboe
parent a6151c3a5c
commit 355b659c87
1 changed files with 9 additions and 0 deletions
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9
block/cfq-iosched.c
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@ -1093,6 +1093,15 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd)
if (!cic || !atomic_read(&cic->ioc->nr_tasks)) if (!cic || !atomic_read(&cic->ioc->nr_tasks))
return; return;
/*
* If our average think time is larger than the remaining time
* slice, then don't idle. This avoids overrunning the allotted
* time slice.
*/
if (sample_valid(cic->ttime_samples) &&
(cfqq->slice_end - jiffies < cic->ttime_mean))
return;
cfq_mark_cfqq_wait_request(cfqq); cfq_mark_cfqq_wait_request(cfqq);
/* /*