From aa1b46dcdc7baaf5fec0be25782ef24b26aa209e Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Sun, 13 Mar 2022 21:15:02 -1000 Subject: block: fix rq-qos breakage from skipping rq_qos_done_bio() a647a524a467 ("block: don't call rq_qos_ops->done_bio if the bio isn't tracked") made bio_endio() skip rq_qos_done_bio() if BIO_TRACKED is not set. While this fixed a potential oops, it also broke blk-iocost by skipping the done_bio callback for merged bios. Before, whether a bio goes through rq_qos_throttle() or rq_qos_merge(), rq_qos_done_bio() would be called on the bio on completion with BIO_TRACKED distinguishing the former from the latter. rq_qos_done_bio() is not called for bios which wenth through rq_qos_merge(). This royally confuses blk-iocost as the merged bios never finish and are considered perpetually in-flight. One reliably reproducible failure mode is an intermediate cgroup geting stuck active preventing its children from being activated due to the leaf-only rule, leading to loss of control. The following is from resctl-bench protection scenario which emulates isolating a web server like workload from a memory bomb run on an iocost configuration which should yield a reasonable level of protection. # cat /sys/block/nvme2n1/device/model Samsung SSD 970 PRO 512GB # cat /sys/fs/cgroup/io.cost.model 259:0 ctrl=user model=linear rbps=834913556 rseqiops=93622 rrandiops=102913 wbps=618985353 wseqiops=72325 wrandiops=71025 # cat /sys/fs/cgroup/io.cost.qos 259:0 enable=1 ctrl=user rpct=95.00 rlat=18776 wpct=95.00 wlat=8897 min=60.00 max=100.00 # resctl-bench -m 29.6G -r out.json run protection::scenario=mem-hog,loops=1 ... Memory Hog Summary ================== IO Latency: R p50=242u:336u/2.5m p90=794u:1.4m/7.5m p99=2.7m:8.0m/62.5m max=8.0m:36.4m/350m W p50=221u:323u/1.5m p90=709u:1.2m/5.5m p99=1.5m:2.5m/9.5m max=6.9m:35.9m/350m Isolation and Request Latency Impact Distributions: min p01 p05 p10 p25 p50 p75 p90 p95 p99 max mean stdev isol% 15.90 15.90 15.90 40.05 57.24 59.07 60.01 74.63 74.63 90.35 90.35 58.12 15.82 lat-imp% 0 0 0 0 0 4.55 14.68 15.54 233.5 548.1 548.1 53.88 143.6 Result: isol=58.12:15.82% lat_imp=53.88%:143.6 work_csv=100.0% missing=3.96% The isolation result of 58.12% is close to what this device would show without any IO control. Fix it by introducing a new flag BIO_QOS_MERGED to mark merged bios and calling rq_qos_done_bio() on them too. For consistency and clarity, rename BIO_TRACKED to BIO_QOS_THROTTLED. The flag checks are moved into rq_qos_done_bio() so that it's next to the code paths that set the flags. With the patch applied, the above same benchmark shows: # resctl-bench -m 29.6G -r out.json run protection::scenario=mem-hog,loops=1 ... Memory Hog Summary ================== IO Latency: R p50=123u:84.4u/985u p90=322u:256u/2.5m p99=1.6m:1.4m/9.5m max=11.1m:36.0m/350m W p50=429u:274u/995u p90=1.7m:1.3m/4.5m p99=3.4m:2.7m/11.5m max=7.9m:5.9m/26.5m Isolation and Request Latency Impact Distributions: min p01 p05 p10 p25 p50 p75 p90 p95 p99 max mean stdev isol% 84.91 84.91 89.51 90.73 92.31 94.49 96.36 98.04 98.71 100.0 100.0 94.42 2.81 lat-imp% 0 0 0 0 0 2.81 5.73 11.11 13.92 17.53 22.61 4.10 4.68 Result: isol=94.42:2.81% lat_imp=4.10%:4.68 work_csv=58.34% missing=0% Signed-off-by: Tejun Heo Fixes: a647a524a467 ("block: don't call rq_qos_ops->done_bio if the bio isn't tracked") Cc: stable@vger.kernel.org # v5.15+ Cc: Ming Lei Cc: Yu Kuai Reviewed-by: Ming Lei Link: https://lore.kernel.org/r/Yi7rdrzQEHjJLGKB@slm.duckdns.org Signed-off-by: Jens Axboe --- block/blk-rq-qos.h | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-) (limited to 'block/blk-rq-qos.h') diff --git a/block/blk-rq-qos.h b/block/blk-rq-qos.h index 3cfbc8668cba..68267007da1c 100644 --- a/block/blk-rq-qos.h +++ b/block/blk-rq-qos.h @@ -177,20 +177,20 @@ static inline void rq_qos_requeue(struct request_queue *q, struct request *rq) __rq_qos_requeue(q->rq_qos, rq); } -static inline void rq_qos_done_bio(struct request_queue *q, struct bio *bio) +static inline void rq_qos_done_bio(struct bio *bio) { - if (q->rq_qos) - __rq_qos_done_bio(q->rq_qos, bio); + if (bio->bi_bdev && (bio_flagged(bio, BIO_QOS_THROTTLED) || + bio_flagged(bio, BIO_QOS_MERGED))) { + struct request_queue *q = bdev_get_queue(bio->bi_bdev); + if (q->rq_qos) + __rq_qos_done_bio(q->rq_qos, 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. - */ if (q->rq_qos) { - bio_set_flag(bio, BIO_TRACKED); + bio_set_flag(bio, BIO_QOS_THROTTLED); __rq_qos_throttle(q->rq_qos, bio); } } @@ -205,8 +205,10 @@ static inline void rq_qos_track(struct request_queue *q, struct request *rq, static inline void rq_qos_merge(struct request_queue *q, struct request *rq, struct bio *bio) { - if (q->rq_qos) + if (q->rq_qos) { + bio_set_flag(bio, BIO_QOS_MERGED); __rq_qos_merge(q->rq_qos, rq, bio); + } } static inline void rq_qos_queue_depth_changed(struct request_queue *q) -- cgit v1.2.3-58-ga151