diff options
| -rw-r--r-- | block/blk-iolatency.c | 122 |
1 files changed, 64 insertions, 58 deletions
diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c index 5b676c7cf2b6..9568bf8dfe82 100644 --- a/block/blk-iolatency.c +++ b/block/blk-iolatency.c @@ -87,7 +87,17 @@ struct iolatency_grp; struct blk_iolatency { struct rq_qos rqos; struct timer_list timer; - atomic_t enabled; + + /* + * ->enabled is the master enable switch gating the throttling logic and + * inflight tracking. The number of cgroups which have iolat enabled is + * tracked in ->enable_cnt, and ->enable is flipped on/off accordingly + * from ->enable_work with the request_queue frozen. For details, See + * blkiolatency_enable_work_fn(). + */ + bool enabled; + atomic_t enable_cnt; + struct work_struct enable_work; }; static inline struct blk_iolatency *BLKIOLATENCY(struct rq_qos *rqos) @@ -95,11 +105,6 @@ static inline struct blk_iolatency *BLKIOLATENCY(struct rq_qos *rqos) return container_of(rqos, struct blk_iolatency, rqos); } -static inline bool blk_iolatency_enabled(struct blk_iolatency *blkiolat) -{ - return atomic_read(&blkiolat->enabled) > 0; -} - struct child_latency_info { spinlock_t lock; @@ -464,7 +469,7 @@ static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio) struct blkcg_gq *blkg = bio->bi_blkg; bool issue_as_root = bio_issue_as_root_blkg(bio); - if (!blk_iolatency_enabled(blkiolat)) + if (!blkiolat->enabled) return; while (blkg && blkg->parent) { @@ -594,7 +599,6 @@ static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio) u64 window_start; u64 now; bool issue_as_root = bio_issue_as_root_blkg(bio); - bool enabled = false; int inflight = 0; blkg = bio->bi_blkg; @@ -605,8 +609,7 @@ static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio) if (!iolat) return; - enabled = blk_iolatency_enabled(iolat->blkiolat); - if (!enabled) + if (!iolat->blkiolat->enabled) return; now = ktime_to_ns(ktime_get()); @@ -645,6 +648,7 @@ static void blkcg_iolatency_exit(struct rq_qos *rqos) struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); del_timer_sync(&blkiolat->timer); + flush_work(&blkiolat->enable_work); blkcg_deactivate_policy(rqos->q, &blkcg_policy_iolatency); kfree(blkiolat); } @@ -716,6 +720,44 @@ next: rcu_read_unlock(); } +/** + * blkiolatency_enable_work_fn - Enable or disable iolatency on the device + * @work: enable_work of the blk_iolatency of interest + * + * iolatency needs to keep track of the number of in-flight IOs per cgroup. This + * is relatively expensive as it involves walking up the hierarchy twice for + * every IO. Thus, if iolatency is not enabled in any cgroup for the device, we + * want to disable the in-flight tracking. + * + * We have to make sure that the counting is balanced - we don't want to leak + * the in-flight counts by disabling accounting in the completion path while IOs + * are in flight. This is achieved by ensuring that no IO is in flight by + * freezing the queue while flipping ->enabled. As this requires a sleepable + * context, ->enabled flipping is punted to this work function. + */ +static void blkiolatency_enable_work_fn(struct work_struct *work) +{ + struct blk_iolatency *blkiolat = container_of(work, struct blk_iolatency, + enable_work); + bool enabled; + + /* + * There can only be one instance of this function running for @blkiolat + * and it's guaranteed to be executed at least once after the latest + * ->enabled_cnt modification. Acting on the latest ->enable_cnt is + * sufficient. + * + * Also, we know @blkiolat is safe to access as ->enable_work is flushed + * in blkcg_iolatency_exit(). + */ + enabled = atomic_read(&blkiolat->enable_cnt); + if (enabled != blkiolat->enabled) { + blk_mq_freeze_queue(blkiolat->rqos.q); + blkiolat->enabled = enabled; + blk_mq_unfreeze_queue(blkiolat->rqos.q); + } +} + int blk_iolatency_init(struct request_queue *q) { struct blk_iolatency *blkiolat; @@ -741,17 +783,15 @@ int blk_iolatency_init(struct request_queue *q) } timer_setup(&blkiolat->timer, blkiolatency_timer_fn, 0); + INIT_WORK(&blkiolat->enable_work, blkiolatency_enable_work_fn); return 0; } -/* - * return 1 for enabling iolatency, return -1 for disabling iolatency, otherwise - * return 0. - */ -static int iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val) +static void iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val) { struct iolatency_grp *iolat = blkg_to_lat(blkg); + struct blk_iolatency *blkiolat = iolat->blkiolat; u64 oldval = iolat->min_lat_nsec; iolat->min_lat_nsec = val; @@ -759,13 +799,15 @@ static int iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val) iolat->cur_win_nsec = min_t(u64, iolat->cur_win_nsec, BLKIOLATENCY_MAX_WIN_SIZE); - if (!oldval && val) - return 1; + if (!oldval && val) { + if (atomic_inc_return(&blkiolat->enable_cnt) == 1) + schedule_work(&blkiolat->enable_work); + } if (oldval && !val) { blkcg_clear_delay(blkg); - return -1; + if (atomic_dec_return(&blkiolat->enable_cnt) == 0) + schedule_work(&blkiolat->enable_work); } - return 0; } static void iolatency_clear_scaling(struct blkcg_gq *blkg) @@ -797,7 +839,6 @@ static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char *buf, u64 lat_val = 0; u64 oldval; int ret; - int enable = 0; ret = blkg_conf_prep(blkcg, &blkcg_policy_iolatency, buf, &ctx); if (ret) @@ -832,41 +873,12 @@ static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char *buf, blkg = ctx.blkg; oldval = iolat->min_lat_nsec; - enable = iolatency_set_min_lat_nsec(blkg, lat_val); - if (enable) { - if (!blk_get_queue(blkg->q)) { - ret = -ENODEV; - goto out; - } - - blkg_get(blkg); - } - - if (oldval != iolat->min_lat_nsec) { + iolatency_set_min_lat_nsec(blkg, lat_val); + if (oldval != iolat->min_lat_nsec) iolatency_clear_scaling(blkg); - } - ret = 0; out: blkg_conf_finish(&ctx); - if (ret == 0 && enable) { - struct iolatency_grp *tmp = blkg_to_lat(blkg); - struct blk_iolatency *blkiolat = tmp->blkiolat; - - blk_mq_freeze_queue(blkg->q); - - if (enable == 1) - atomic_inc(&blkiolat->enabled); - else if (enable == -1) - atomic_dec(&blkiolat->enabled); - else - WARN_ON_ONCE(1); - - blk_mq_unfreeze_queue(blkg->q); - - blkg_put(blkg); - blk_put_queue(blkg->q); - } return ret ?: nbytes; } @@ -1005,14 +1017,8 @@ static void iolatency_pd_offline(struct blkg_policy_data *pd) { struct iolatency_grp *iolat = pd_to_lat(pd); struct blkcg_gq *blkg = lat_to_blkg(iolat); - struct blk_iolatency *blkiolat = iolat->blkiolat; - int ret; - ret = iolatency_set_min_lat_nsec(blkg, 0); - if (ret == 1) - atomic_inc(&blkiolat->enabled); - if (ret == -1) - atomic_dec(&blkiolat->enabled); + iolatency_set_min_lat_nsec(blkg, 0); iolatency_clear_scaling(blkg); } |