| Message ID | Yi7rdrzQEHjJLGKB@slm.duckdns.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [block-5.17] fix rq-qos breakage from skipping rq_qos_done_bio() | expand |
Ah, I forgot "block: " in the subject line. Please let me know if you want the patch resent. Thanks.
On Sun, Mar 13, 2022 at 09:15:02PM -1000, Tejun Heo wrote: > 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 <tj@kernel.org> > 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 <ming.lei@redhat.com> > Cc: Yu Kuai <yukuai3@huawei.com> Looks fine since rq always holds one .q_usage_counter in case of merge: Reviewed-by: Ming Lei <ming.lei@redhat.com> Thanks, Ming
On Sun, 13 Mar 2022 21:15:02 -1000, Tejun Heo wrote: > 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. > > [...] Applied, thanks! [1/1] fix rq-qos breakage from skipping rq_qos_done_bio() (no commit info) Best regards,
--- a/block/bio.c +++ b/block/bio.c @@ -1486,8 +1486,7 @@ again: if (!bio_integrity_endio(bio)) return; - if (bio->bi_bdev && bio_flagged(bio, BIO_TRACKED)) - rq_qos_done_bio(bdev_get_queue(bio->bi_bdev), bio); + rq_qos_done_bio(bio); if (bio->bi_bdev && bio_flagged(bio, BIO_TRACE_COMPLETION)) { trace_block_bio_complete(bdev_get_queue(bio->bi_bdev), bio); --- a/block/blk-iolatency.c +++ b/block/blk-iolatency.c @@ -598,7 +598,7 @@ static void blkcg_iolatency_done_bio(str int inflight = 0; blkg = bio->bi_blkg; - if (!blkg || !bio_flagged(bio, BIO_TRACKED)) + if (!blkg || !bio_flagged(bio, BIO_QOS_THROTTLED)) return; iolat = blkg_to_lat(bio->bi_blkg); --- a/block/blk-rq-qos.h +++ b/block/blk-rq-qos.h @@ -177,20 +177,20 @@ static inline void rq_qos_requeue(struct __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 r 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) --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -317,7 +317,8 @@ enum { BIO_TRACE_COMPLETION, /* bio_endio() should trace the final completion * of this bio. */ BIO_CGROUP_ACCT, /* has been accounted to a cgroup */ - BIO_TRACKED, /* set if bio goes through the rq_qos path */ + BIO_QOS_THROTTLED, /* bio went through rq_qos throttle path */ + BIO_QOS_MERGED, /* but went through rq_qos merge path */ BIO_REMAPPED, BIO_ZONE_WRITE_LOCKED, /* Owns a zoned device zone write lock */ BIO_PERCPU_CACHE, /* can participate in per-cpu alloc cache */
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 <tj@kernel.org> 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 <ming.lei@redhat.com> Cc: Yu Kuai <yukuai3@huawei.com> --- block/bio.c | 3 +-- block/blk-iolatency.c | 2 +- block/blk-rq-qos.h | 20 +++++++++++--------- include/linux/blk_types.h | 3 ++- 4 files changed, 15 insertions(+), 13 deletions(-)