| From 757574b0b51687473de1009bb5101ff1e464513b Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Mon, 2 Aug 2021 16:13:52 +0200 |
| Subject: block, bfq: honor already-setup queue merges |
| |
| From: Paolo Valente <paolo.valente@linaro.org> |
| |
| [ Upstream commit 2d52c58b9c9bdae0ca3df6a1eab5745ab3f7d80b ] |
| |
| The function bfq_setup_merge prepares the merging between two |
| bfq_queues, say bfqq and new_bfqq. To this goal, it assigns |
| bfqq->new_bfqq = new_bfqq. Then, each time some I/O for bfqq arrives, |
| the process that generated that I/O is disassociated from bfqq and |
| associated with new_bfqq (merging is actually a redirection). In this |
| respect, bfq_setup_merge increases new_bfqq->ref in advance, adding |
| the number of processes that are expected to be associated with |
| new_bfqq. |
| |
| Unfortunately, the stable-merging mechanism interferes with this |
| setup. After bfqq->new_bfqq has been set by bfq_setup_merge, and |
| before all the expected processes have been associated with |
| bfqq->new_bfqq, bfqq may happen to be stably merged with a different |
| queue than the current bfqq->new_bfqq. In this case, bfqq->new_bfqq |
| gets changed. So, some of the processes that have been already |
| accounted for in the ref counter of the previous new_bfqq will not be |
| associated with that queue. This creates an unbalance, because those |
| references will never be decremented. |
| |
| This commit fixes this issue by reestablishing the previous, natural |
| behaviour: once bfqq->new_bfqq has been set, it will not be changed |
| until all expected redirections have occurred. |
| |
| Signed-off-by: Davide Zini <davidezini2@gmail.com> |
| Signed-off-by: Paolo Valente <paolo.valente@linaro.org> |
| Link: https://lore.kernel.org/r/20210802141352.74353-2-paolo.valente@linaro.org |
| Signed-off-by: Jens Axboe <axboe@kernel.dk> |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| block/bfq-iosched.c | 16 +++++++++++++--- |
| 1 file changed, 13 insertions(+), 3 deletions(-) |
| |
| diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c |
| index 9360c65169ff..3a1038b6eeb3 100644 |
| --- a/block/bfq-iosched.c |
| +++ b/block/bfq-iosched.c |
| @@ -2662,6 +2662,15 @@ bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq) |
| * are likely to increase the throughput. |
| */ |
| bfqq->new_bfqq = new_bfqq; |
| + /* |
| + * The above assignment schedules the following redirections: |
| + * each time some I/O for bfqq arrives, the process that |
| + * generated that I/O is disassociated from bfqq and |
| + * associated with new_bfqq. Here we increases new_bfqq->ref |
| + * in advance, adding the number of processes that are |
| + * expected to be associated with new_bfqq as they happen to |
| + * issue I/O. |
| + */ |
| new_bfqq->ref += process_refs; |
| return new_bfqq; |
| } |
| @@ -2724,6 +2733,10 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, |
| { |
| struct bfq_queue *in_service_bfqq, *new_bfqq; |
| |
| + /* if a merge has already been setup, then proceed with that first */ |
| + if (bfqq->new_bfqq) |
| + return bfqq->new_bfqq; |
| + |
| /* |
| * Check delayed stable merge for rotational or non-queueing |
| * devs. For this branch to be executed, bfqq must not be |
| @@ -2825,9 +2838,6 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, |
| if (bfq_too_late_for_merging(bfqq)) |
| return NULL; |
| |
| - if (bfqq->new_bfqq) |
| - return bfqq->new_bfqq; |
| - |
| if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq)) |
| return NULL; |
| |
| -- |
| 2.30.2 |
| |
