diff options
| -rw-r--r-- | block/bfq-iosched.c | 36 |
1 files changed, 33 insertions, 3 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 3f32e88c7e9b..4fd4f1996498 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -3597,8 +3597,14 @@ static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd) bfq_log_bfqq(bfqd, bfqq, "select_queue: already in-service queue"); + /* + * Do not expire bfqq for budget timeout if bfqq may be about + * to enjoy device idling. The reason why, in this case, we + * prevent bfqq from expiring is the same as in the comments + * on the case where bfq_bfqq_must_idle() returns true, in + * bfq_completed_request(). + */ if (bfq_may_expire_for_budg_timeout(bfqq) && - !bfq_bfqq_wait_request(bfqq) && !bfq_bfqq_must_idle(bfqq)) goto expire; @@ -4674,8 +4680,32 @@ static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd) * or if we want to idle in case it has no pending requests. */ if (bfqd->in_service_queue == bfqq) { - if (bfqq->dispatched == 0 && bfq_bfqq_must_idle(bfqq)) { - bfq_arm_slice_timer(bfqd); + if (bfq_bfqq_must_idle(bfqq)) { + if (bfqq->dispatched == 0) + bfq_arm_slice_timer(bfqd); + /* + * If we get here, we do not expire bfqq, even + * if bfqq was in budget timeout or had no + * more requests (as controlled in the next + * conditional instructions). The reason for + * not expiring bfqq is as follows. + * + * Here bfqq->dispatched > 0 holds, but + * bfq_bfqq_must_idle() returned true. This + * implies that, even if no request arrives + * for bfqq before bfqq->dispatched reaches 0, + * bfqq will, however, not be expired on the + * completion event that causes bfqq->dispatch + * to reach zero. In contrast, on this event, + * bfqq will start enjoying device idling + * (I/O-dispatch plugging). + * + * But, if we expired bfqq here, bfqq would + * not have the chance to enjoy device idling + * when bfqq->dispatched finally reaches + * zero. This would expose bfqq to violation + * of its reserved service guarantees. + */ return; } else if (bfq_may_expire_for_budg_timeout(bfqq)) bfq_bfqq_expire(bfqd, bfqq, false, |