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| author | Dennis Zhou <dennis@kernel.org> | 2018-12-17 11:03:51 -0500 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2018-12-17 11:19:54 -0700 |
| commit | 13369816cb648f897ce9cbf57e55eeb742ce4eb3 (patch) | |
| tree | 767ad29aad32298bd4760aead21632ee205f2ffb | |
| parent | c16d6b5a9f47d0e581882269fca1d73be60208b2 (diff) | |
| download | blackbird-obmc-linux-13369816cb648f897ce9cbf57e55eeb742ce4eb3.tar.gz blackbird-obmc-linux-13369816cb648f897ce9cbf57e55eeb742ce4eb3.zip | |
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>
| -rw-r--r-- | block/blk-iolatency.c | 2 | ||||
| -rw-r--r-- | block/blk-rq-qos.h | 5 | ||||
| -rw-r--r-- | include/linux/blk_types.h | 1 |
3 files changed, 7 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); 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); } diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index 46c005d601ac..fc99474ac968 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -228,6 +228,7 @@ struct bio { #define BIO_TRACE_COMPLETION 10 /* bio_endio() should trace the final completion * of this bio. */ #define BIO_QUEUE_ENTERED 11 /* can use blk_queue_enter_live() */ +#define BIO_TRACKED 12 /* set if bio goes through the rq_qos path */ /* See BVEC_POOL_OFFSET below before adding new flags */ |
