| From 41e76c85660c022c6bf5713bfb6c21e64a487cec Mon Sep 17 00:00:00 2001 |
| From: Jan Kara <jack@suse.cz> |
| Date: Fri, 5 Jun 2020 16:16:16 +0200 |
| Subject: bfq: Avoid false bfq queue merging |
| |
| From: Jan Kara <jack@suse.cz> |
| |
| commit 41e76c85660c022c6bf5713bfb6c21e64a487cec upstream. |
| |
| bfq_setup_cooperator() uses bfqd->in_serv_last_pos so detect whether it |
| makes sense to merge current bfq queue with the in-service queue. |
| However if the in-service queue is freshly scheduled and didn't dispatch |
| any requests yet, bfqd->in_serv_last_pos is stale and contains value |
| from the previously scheduled bfq queue which can thus result in a bogus |
| decision that the two queues should be merged. This bug can be observed |
| for example with the following fio jobfile: |
| |
| [global] |
| direct=0 |
| ioengine=sync |
| invalidate=1 |
| size=1g |
| rw=read |
| |
| [reader] |
| numjobs=4 |
| directory=/mnt |
| |
| where the 4 processes will end up in the one shared bfq queue although |
| they do IO to physically very distant files (for some reason I was able to |
| observe this only with slice_idle=1ms setting). |
| |
| Fix the problem by invalidating bfqd->in_serv_last_pos when switching |
| in-service queue. |
| |
| Fixes: 058fdecc6de7 ("block, bfq: fix in-service-queue check for queue merging") |
| CC: stable@vger.kernel.org |
| Signed-off-by: Jan Kara <jack@suse.cz> |
| Acked-by: Paolo Valente <paolo.valente@linaro.org> |
| Signed-off-by: Jens Axboe <axboe@kernel.dk> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| block/bfq-iosched.c | 1 + |
| 1 file changed, 1 insertion(+) |
| |
| --- a/block/bfq-iosched.c |
| +++ b/block/bfq-iosched.c |
| @@ -2478,6 +2478,7 @@ static void __bfq_set_in_service_queue(s |
| } |
| |
| bfqd->in_service_queue = bfqq; |
| + bfqd->in_serv_last_pos = 0; |
| } |
| |
| /* |
