summaryrefslogtreecommitdiff
diff options
context:
space:
mode:
-rw-r--r--block/bfq-iosched.c36
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,