diff options
| -rw-r--r-- | block/cfq-iosched.c | 54 |
1 files changed, 48 insertions, 6 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index f41fdb5f3e0..98b15b98b85 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -2141,8 +2141,22 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd) /* * The active queue has run out of time, expire it and select new. */ - if (cfq_slice_used(cfqq) && !cfq_cfqq_must_dispatch(cfqq)) - goto expire; + if (cfq_slice_used(cfqq) && !cfq_cfqq_must_dispatch(cfqq)) { + /* + * If slice had not expired at the completion of last request + * we might not have turned on wait_busy flag. Don't expire + * the queue yet. Allow the group to get backlogged. + * + * The very fact that we have used the slice, that means we + * have been idling all along on this queue and it should be + * ok to wait for this request to complete. + */ + if (cfqq->cfqg->nr_cfqq == 1 && cfqq->dispatched + && cfq_should_idle(cfqd, cfqq)) + goto keep_queue; + else + goto expire; + } /* * The active queue has requests and isn't expired, allow it to @@ -3256,6 +3270,35 @@ static void cfq_update_hw_tag(struct cfq_data *cfqd) cfqd->hw_tag = 0; } +static bool cfq_should_wait_busy(struct cfq_data *cfqd, struct cfq_queue *cfqq) +{ + struct cfq_io_context *cic = cfqd->active_cic; + + /* If there are other queues in the group, don't wait */ + if (cfqq->cfqg->nr_cfqq > 1) + return false; + + if (cfq_slice_used(cfqq)) + return true; + + /* if slice left is less than think time, wait busy */ + if (cic && sample_valid(cic->ttime_samples) + && (cfqq->slice_end - jiffies < cic->ttime_mean)) + return true; + + /* + * If think times is less than a jiffy than ttime_mean=0 and above + * will not be true. It might happen that slice has not expired yet + * but will expire soon (4-5 ns) during select_queue(). To cover the + * case where think time is less than a jiffy, mark the queue wait + * busy if only 1 jiffy is left in the slice. + */ + if (cfqq->slice_end - jiffies == 1) + return true; + + return false; +} + static void cfq_completed_request(struct request_queue *q, struct request *rq) { struct cfq_queue *cfqq = RQ_CFQQ(rq); @@ -3295,11 +3338,10 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq) } /* - * If this queue consumed its slice and this is last queue - * in the group, wait for next request before we expire - * the queue + * Should we wait for next request to come in before we expire + * the queue. */ - if (cfq_slice_used(cfqq) && cfqq->cfqg->nr_cfqq == 1) { + if (cfq_should_wait_busy(cfqd, cfqq)) { cfqq->slice_end = jiffies + cfqd->cfq_slice_idle; cfq_mark_cfqq_wait_busy(cfqq); } |