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, to tag all bios w/ blkgs in [1] changed the timing incorrectly as well. First, the iolatency controller was tagging bios and using that information if it should process it in rq_qos_done_bio(). However, now that all bios are tagged, this caused the atomic_t for the struct rq_wait inflight count to underflow resulting in a stall. Second, now the timing was using the duration a bio from generic_make_request() rather than the timing mentioned above. This patch fixes the errors by accounting time separately in a bio adding the field bi_start. If this field is set, the bio should be processed by blk-iolatency in rq_qos_done_bio(). [1] https://lore.kernel.org/lkml/20181205171039.73066-1-den...@kernel.org/ Signed-off-by: Dennis Zhou <den...@kernel.org> Cc: Josef Bacik <jo...@toxicpanda.com> --- block/blk-iolatency.c | 17 ++++++----------- include/linux/blk_types.h | 12 ++++++++++++ 2 files changed, 18 insertions(+), 11 deletions(-) diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c index bee092727cad..52d5d7cc387c 100644 --- a/block/blk-iolatency.c +++ b/block/blk-iolatency.c @@ -463,6 +463,8 @@ static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio) if (!blk_iolatency_enabled(blkiolat)) return; + bio->bi_start = ktime_get_ns(); + while (blkg && blkg->parent) { struct iolatency_grp *iolat = blkg_to_lat(blkg); if (!iolat) { @@ -480,18 +482,12 @@ static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio) } static void iolatency_record_time(struct iolatency_grp *iolat, - struct bio_issue *issue, u64 now, + struct bio *bio, u64 now, bool issue_as_root) { - u64 start = bio_issue_time(issue); + u64 start = bio->bi_start; u64 req_time; - /* - * Have to do this so we are truncated to the correct time that our - * issue is truncated to. - */ - now = __bio_issue_time(now); - if (now <= start) return; @@ -593,7 +589,7 @@ 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->bi_start) return; iolat = blkg_to_lat(bio->bi_blkg); @@ -612,8 +608,7 @@ static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio) atomic_dec(&rqw->inflight); if (!enabled || iolat->min_lat_nsec == 0) goto next; - iolatency_record_time(iolat, &bio->bi_issue, now, - issue_as_root); + iolatency_record_time(iolat, bio, now, issue_as_root); window_start = atomic64_read(&iolat->window_start); if (now > window_start && (now - window_start) >= iolat->cur_win_nsec) { diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index 46c005d601ac..c2c02ec08d7c 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -181,6 +181,18 @@ struct bio { */ struct blkcg_gq *bi_blkg; struct bio_issue bi_issue; +#ifdef CONFIG_BLK_CGROUP_IOLATENCY + /* + * blk-iolatency measure the time a bio takes between rq_qos_throttle() + * and rq_qos_done_bio(). It attributes the time to the bio that gets + * the request allowing any bios that can tag along via plug merging or + * bio merging to be free (from blk-iolatency's perspective). This is + * different from the time a bio takes from generic_make_request() to + * the end of its life. So, this also serves as a marker for which bios + * should be processed by blk-iolatency. + */ + u64 bi_start; +#endif /* CONFIG_BLK_CGROUP_IOLATENCY */ #endif union { #if defined(CONFIG_BLK_DEV_INTEGRITY) -- 2.17.1
