From 85686d0dc1946bd9903efb1c130d634f963e4843 Mon Sep 17 00:00:00 2001 From: Paolo Valente Date: Thu, 4 Mar 2021 18:46:26 +0100 Subject: block, bfq: keep shared queues out of the waker mechanism Shared queues are likely to receive I/O at a high rate. This may deceptively let them be considered as wakers of other queues. But a false waker will unjustly steal bandwidth to its supposedly woken queue. So considering also shared queues in the waking mechanism may cause more control troubles than throughput benefits. This commit keeps shared queues out of the waker-detection mechanism. Tested-by: Jan Kara Signed-off-by: Paolo Valente Tested-by: Oleksandr Natalenko Link: https://lore.kernel.org/r/20210304174627.161-6-paolo.valente@linaro.org Signed-off-by: Jens Axboe --- block/bfq-iosched.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) (limited to 'block') diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 2a84294b0525..a3f59d3065b3 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -5860,7 +5860,17 @@ static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd) 1UL<<(BFQ_RATE_SHIFT - 10)) bfq_update_rate_reset(bfqd, NULL); bfqd->last_completion = now_ns; - bfqd->last_completed_rq_bfqq = bfqq; + /* + * Shared queues are likely to receive I/O at a high + * rate. This may deceptively let them be considered as wakers + * of other queues. But a false waker will unjustly steal + * bandwidth to its supposedly woken queue. So considering + * also shared queues in the waking mechanism may cause more + * control troubles than throughput benefits. Then do not set + * last_completed_rq_bfqq to bfqq if bfqq is a shared queue. + */ + if (!bfq_bfqq_coop(bfqq)) + bfqd->last_completed_rq_bfqq = bfqq; /* * If we are waiting to discover whether the request pattern -- cgit v1.2.3-59-g8ed1b