From 9a2ac41b13c573703d6689f51f3e27dd658324be Mon Sep 17 00:00:00 2001 From: Paolo Valente Date: Sat, 19 Jun 2021 16:09:48 +0200 Subject: [PATCH] block, bfq: reset waker pointer with shared queues Commit 85686d0dc194 ("block, bfq: keep shared queues out of the waker mechanism") leaves shared bfq_queues out of the waker-detection mechanism. It attains this goal by not updating the pointer last_completed_rq_bfqq, if the last request completed belongs to a shared bfq_queue (so that the pointer will not point to the shared bfq_queue). Yet this has a side effect: the pointer last_completed_rq_bfqq keeps pointing, deceptively, to a bfq_queue that actually is not the last one to have had a request completed. As a consequence, such a bfq_queue may deceptively be considered as a waker of some bfq_queue, even of some shared bfq_queue. To address this issue, reset last_completed_rq_bfqq if the last request completed belongs to a shared queue. Fixes: 85686d0dc194 ("block, bfq: keep shared queues out of the waker mechanism") Signed-off-by: Paolo Valente Link: https://lore.kernel.org/r/20210619140948.98712-8-paolo.valente@linaro.org Signed-off-by: Jens Axboe --- block/bfq-iosched.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index a273b2bcea2a..fedb0a8fd388 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -6165,11 +6165,13 @@ static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd) * 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. + * control troubles than throughput benefits. Then reset + * last_completed_rq_bfqq if bfqq is a shared queue. */ if (!bfq_bfqq_coop(bfqq)) bfqd->last_completed_rq_bfqq = bfqq; + else + bfqd->last_completed_rq_bfqq = NULL; /* * If we are waiting to discover whether the request pattern -- 2.11.0