diff options
author | Dennis Zhou <dennis@kernel.org> | 2018-12-17 19:03:51 +0300 |
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committer | Jens Axboe <axboe@kernel.dk> | 2018-12-17 21:19:54 +0300 |
commit | 13369816cb648f897ce9cbf57e55eeb742ce4eb3 (patch) | |
tree | 767ad29aad32298bd4760aead21632ee205f2ffb /block/blk-rq-qos.h | |
parent | c16d6b5a9f47d0e581882269fca1d73be60208b2 (diff) | |
download | linux-13369816cb648f897ce9cbf57e55eeb742ce4eb3.tar.xz |
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-rq-qos.h')
-rw-r--r-- | block/blk-rq-qos.h | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/block/blk-rq-qos.h b/block/blk-rq-qos.h index 3c85f26d3846..564851889550 100644 --- a/block/blk-rq-qos.h +++ b/block/blk-rq-qos.h @@ -168,6 +168,11 @@ static inline void rq_qos_done_bio(struct request_queue *q, struct bio *bio) static inline void rq_qos_throttle(struct request_queue *q, struct bio *bio) { + /* + * BIO_TRACKED lets controllers know that a bio went through the + * normal rq_qos path. + */ + bio_set_flag(bio, BIO_TRACKED); if (q->rq_qos) __rq_qos_throttle(q->rq_qos, bio); } |