From d4f49983fa3944416c28379c35fbe10c68455ea4 Mon Sep 17 00:00:00 2001 From: Paolo Valente Date: Sat, 19 Jun 2021 16:09:44 +0200 Subject: 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: https://lore.kernel.org/r/20210619140948.98712-4-paolo.valente@linaro.org Signed-off-by: Jens Axboe --- block/bfq-iosched.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'block/bfq-iosched.c') 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 = bic->stable_merge_bfqq; int proc_ref = min(bfqq_process_refs(bfqq), -- cgit v1.2.3