From: Jan Kara jack@suse.cz
[ Upstream commit f950667356ce90a41b446b726d4595a10cb65415 ]
Currently we look for waker only if current queue has no requests. This makes sense for bfq queues with a single process however for shared queues when there is a larger number of processes the condition that queue has no requests is difficult to meet because often at least one process has some request in flight although all the others are waiting for the waker to do the work and this harms throughput. Relax the "no queued request for bfq queue" condition to "the current task has no queued requests yet". For this, we also need to start tracking number of requests in flight for each task.
This patch (together with the following one) restores the performance for dbench with 128 clients that regressed with commit c65e6fd460b4 ("bfq: Do not let waker requests skip proper accounting") because this commit makes requests of wakers properly enter BFQ queues and thus these queues become ineligible for the old waker detection logic. Dbench results:
Vanilla 5.18-rc3 5.18-rc3 + revert 5.18-rc3 patched Mean 1237.36 ( 0.00%) 950.16 * 23.21%* 988.35 * 20.12%*
Numbers are time to complete workload so lower is better.
Fixes: c65e6fd460b4 ("bfq: Do not let waker requests skip proper accounting") Signed-off-by: Jan Kara jack@suse.cz Link: https://lore.kernel.org/r/20220519105235.31397-1-jack@suse.cz Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/bfq-iosched.c | 5 +++-- block/bfq-iosched.h | 1 + 2 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 963f9f549232..047368c23984 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -2133,7 +2133,6 @@ static void bfq_check_waker(struct bfq_data *bfqd, struct bfq_queue *bfqq, if (!bfqd->last_completed_rq_bfqq || bfqd->last_completed_rq_bfqq == bfqq || bfq_bfqq_has_short_ttime(bfqq) || - bfqq->dispatched > 0 || now_ns - bfqd->last_completion >= 4 * NSEC_PER_MSEC || bfqd->last_completed_rq_bfqq == bfqq->waker_bfqq) return; @@ -2210,7 +2209,7 @@ static void bfq_add_request(struct request *rq) bfqq->queued[rq_is_sync(rq)]++; bfqd->queued++;
- if (RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_bfqq_sync(bfqq)) { + if (bfq_bfqq_sync(bfqq) && RQ_BIC(rq)->requests <= 1) { bfq_check_waker(bfqd, bfqq, now_ns);
/* @@ -6563,6 +6562,7 @@ static void bfq_finish_requeue_request(struct request *rq) bfq_completed_request(bfqq, bfqd); } bfq_finish_requeue_request_body(bfqq); + RQ_BIC(rq)->requests--; spin_unlock_irqrestore(&bfqd->lock, flags);
/* @@ -6796,6 +6796,7 @@ static struct bfq_queue *bfq_init_rq(struct request *rq)
bfqq_request_allocated(bfqq); bfqq->ref++; + bic->requests++; bfq_log_bfqq(bfqd, bfqq, "get_request %p: bfqq %p, %d", rq, bfqq, bfqq->ref);
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h index 07288b9da389..a1ec70af64c8 100644 --- a/block/bfq-iosched.h +++ b/block/bfq-iosched.h @@ -469,6 +469,7 @@ struct bfq_io_cq { struct bfq_queue *stable_merge_bfqq;
bool stably_merged; /* non splittable if true */ + unsigned int requests; /* Number of requests this process has in flight */ };
/**