diff options
authorPaolo Valente <>2021-06-19 16:09:44 +0200
committerJens Axboe <>2021-06-21 15:03:41 -0600
commitd4f49983fa3944416c28379c35fbe10c68455ea4 (patch)
parente03f2ab78a4a673e4af23c3b855591c48b9de4d7 (diff)
block, bfq: consider also creation time in delayed stable merge
Since commit 430a67f9d616 ("block, bfq: merge bursts of newly-created queues"), BFQ may schedule a merge between a newly created sync bfq_queue and the last sync bfq_queue created. Such a merging is not performed immediately, because BFQ needs first to find out whether the newly created queue actually reaches a higher throughput if not merged at all (and in that case BFQ will not perform any stable merging). To check that, a little time must be waited after the creation of the new queue, so that some I/O can flow in the queue, and statistics on such I/O can be computed. Yet, to evaluate the above waiting time, the last split time is considered as start time, instead of the creation time of the queue. This is a mistake, because considering the split time is correct only in the following scenario. The queue undergoes a non-stable merges on the arrival of its very first I/O request, due to close I/O with some other queue. While the queue is merged for close I/O, stable merging is not considered. Yet the queue may then happen to be split, if the close I/O finishes (or happens to be a false positive). From this time on, the queue can again be considered for stable merging. But, again, a little time must elapse, to let some new I/O flow in the queue and to get updated statistics. To wait for this time, the split time is to be taken into account. Yet, if the queue does not undergo a non-stable merge on the arrival of its very first request, then BFQ immediately checks whether the stable merge is to be performed. It happens because the split time for a queue is initialized to minus infinity when the queue is created. This commit fixes this mistake by adding the missing condition. Now the check for delayed stable-merge is performed after a little time is elapsed not only from the last queue split time, but also from the creation time of the queue. Fixes: 430a67f9d616 ("block, bfq: merge bursts of newly-created queues") Signed-off-by: Paolo Valente <> Link: Signed-off-by: Jens Axboe <>
1 files changed, 3 insertions, 1 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index c5c0e74977d4..2a5c1a660f3b 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2711,7 +2711,9 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
if (bic->stable_merge_bfqq &&
!bfq_bfqq_just_created(bfqq) &&
time_is_before_jiffies(bfqq->split_time +
- msecs_to_jiffies(200))) {
+ msecs_to_jiffies(200)) &&
+ time_is_before_jiffies(bfqq->creation_time +
+ msecs_to_jiffies(200))) {
struct bfq_queue *stable_merge_bfqq =
int proc_ref = min(bfqq_process_refs(bfqq),