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| author | Paolo Valente <paolo.valente@linaro.org> | 2021-06-19 16:09:44 +0200 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2021-06-21 15:03:41 -0600 |
| commit | d4f49983fa3944416c28379c35fbe10c68455ea4 (patch) | |
| tree | a8206f39b43a37693755e3f8b0d9fdd6e531e2ba /block | |
| parent | e03f2ab78a4a673e4af23c3b855591c48b9de4d7 (diff) | |
| download | linux-d4f49983fa3944416c28379c35fbe10c68455ea4.tar.gz | |
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 <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20210619140948.98712-4-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
| -rw-r--r-- | block/bfq-iosched.c | 4 |
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 = bic->stable_merge_bfqq; int proc_ref = min(bfqq_process_refs(bfqq), |