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authorPaolo Valente <paolo.valente@linaro.org>2021-03-04 18:46:26 +0100
committerJens Axboe <axboe@kernel.dk>2021-03-25 17:50:07 +0100
commit85686d0dc1946bd9903efb1c130d634f963e4843 (patch)
tree83e13d8f7939dc4aecbd9af7a546b9486d53b77b
parentblock, bfq: fix weight-raising resume with !low_latency (diff)
downloadlinux-85686d0dc1946bd9903efb1c130d634f963e4843.tar.xz
linux-85686d0dc1946bd9903efb1c130d634f963e4843.zip
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 <jack@suse.cz> Signed-off-by: Paolo Valente <paolo.valente@linaro.org> Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name> Link: https://lore.kernel.org/r/20210304174627.161-6-paolo.valente@linaro.org Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--block/bfq-iosched.c12
1 files changed, 11 insertions, 1 deletions
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