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authorPaolo Valente <paolo.valente@linaro.org>2019-01-29 12:06:38 +0100
committerJens Axboe <axboe@kernel.dk>2019-01-31 12:50:24 -0700
commit058fdecc6de7cdecbf4c59b851e80eb2d6c5295f (patch)
treee48869ade51d46200381586259daf112a14302d3 /block
parent02a6d787f4afc8be2d3d52ab0a1df0c6a2d99e7b (diff)
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block, bfq: fix in-service-queue check for queue merging
When a new I/O request arrives for a bfq_queue, say Q, bfq checks whether that request is close to (a) the head request of some other queue waiting to be served, or (b) the last request dispatched for the in-service queue (in case Q itself is not the in-service queue) If a queue, say Q2, is found for which the above condition holds, then bfq merges Q and Q2, to hopefully get a more sequential I/O in the resulting merged queue, and thus a possibly higher throughput. Case (b) is checked by comparing the new request for Q with the last request dispatched, assuming that the latter necessarily belonged to the in-service queue. Unfortunately, this assumption is no longer always correct, since commit d0edc2473be9 ("block, bfq: inject other-queue I/O into seeky idle queues on NCQ flash"). When the assumption does not hold, queues that must not be merged may be merged, causing unexpected loss of control on per-queue service guarantees. This commit solves this problem by adding an extra field, which stores the actual last request dispatched for the in-service queue, and by using this new field to correctly check case (b). Signed-off-by: Paolo Valente <paolo.valente@linaro.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
-rw-r--r--block/bfq-iosched.c5
-rw-r--r--block/bfq-iosched.h3
2 files changed, 7 insertions, 1 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 06268449d2ca..4c592496a16a 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2251,7 +2251,8 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
if (in_service_bfqq && in_service_bfqq != bfqq &&
likely(in_service_bfqq != &bfqd->oom_bfqq) &&
- bfq_rq_close_to_sector(io_struct, request, bfqd->last_position) &&
+ bfq_rq_close_to_sector(io_struct, request,
+ bfqd->in_serv_last_pos) &&
bfqq->entity.parent == in_service_bfqq->entity.parent &&
bfq_may_be_close_cooperator(bfqq, in_service_bfqq)) {
new_bfqq = bfq_setup_merge(bfqq, in_service_bfqq);
@@ -2791,6 +2792,8 @@ update_rate_and_reset:
bfq_update_rate_reset(bfqd, rq);
update_last_values:
bfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
+ if (RQ_BFQQ(rq) == bfqd->in_service_queue)
+ bfqd->in_serv_last_pos = bfqd->last_position;
bfqd->last_dispatch = now_ns;
}
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 30be669be465..062e1c4787f4 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -538,6 +538,9 @@ struct bfq_data {
/* on-disk position of the last served request */
sector_t last_position;
+ /* position of the last served request for the in-service queue */
+ sector_t in_serv_last_pos;
+
/* time of last request completion (ns) */
u64 last_completion;