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author | Dennis Zhou <dennis@kernel.org> | 2018-12-17 11:03:51 -0500 |
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committer | Jens Axboe <axboe@kernel.dk> | 2018-12-17 11:19:54 -0700 |
commit | 13369816cb648f897ce9cbf57e55eeb742ce4eb3 (patch) | |
tree | 767ad29aad32298bd4760aead21632ee205f2ffb /block/blk-iolatency.c | |
parent | c16d6b5a9f47d0e581882269fca1d73be60208b2 (diff) | |
download | linux-13369816cb648f897ce9cbf57e55eeb742ce4eb3.tar.gz |
block: fix blk-iolatency accounting underflow
The blk-iolatency controller measures the time from rq_qos_throttle() to rq_qos_done_bio() and attributes this time to the first bio that needs to create the request. This means if a bio is plug-mergeable or bio-mergeable, it gets to bypass the blk-iolatency controller. The recent series [1], to tag all bios w/ blkgs undermined how iolatency was determining which bios it was charging and should process in rq_qos_done_bio(). Because all bios are being tagged, this caused the atomic_t for the struct rq_wait inflight count to underflow and result in a stall. This patch adds a new flag BIO_TRACKED to let controllers know that a bio is going through the rq_qos path. blk-iolatency now checks if this flag is set to see if it should process the bio in rq_qos_done_bio(). Overloading BLK_QUEUE_ENTERED works, but makes the flag rules confusing. BIO_THROTTLED was another candidate, but the flag is set for all bios that have gone through blk-throttle code. Overloading a flag comes with the burden of making sure that when either implementation changes, a change in setting rules for one doesn't cause a bug in the other. So here, we unfortunately opt for adding a new flag. [1] https://lore.kernel.org/lkml/20181205171039.73066-1-dennis@kernel.org/ Fixes: 5cdf2e3fea5e ("blkcg: associate blkg when associating a device") Signed-off-by: Dennis Zhou <dennis@kernel.org> Cc: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-iolatency.c')
-rw-r--r-- | block/blk-iolatency.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c index bee092727cad..fc714ef402a6 100644 --- a/block/blk-iolatency.c +++ b/block/blk-iolatency.c @@ -593,7 +593,7 @@ static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio) bool enabled = false; blkg = bio->bi_blkg; - if (!blkg) + if (!blkg || !bio_flagged(bio, BIO_TRACKED)) return; iolat = blkg_to_lat(bio->bi_blkg); |