From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx> The iocost rely on rq start_time_ns and alloc_time_ns to tell saturation state of the block device. Most of the time request is allocated after rq_qos_throttle() and its alloc_time_ns or start_time_ns won't be affected. But for plug batched allocation introduced by the commit 47c122e35d7e ("block: pre-allocate requests if plug is started and is a batch"), we can rq_qos_throttle() after the allocation of the request. This is what the blk_mq_get_cached_request() does. In this case, the cached request alloc_time_ns or start_time_ns is much ahead if blocked in any qos ->throttle(). This patch fix it by setting alloc_time_ns and start_time_ns to now when the pre-allocated rq is actually used. And we skip setting the alloc_time_ns and start_time_ns during pre-allocation, so just pass 0 in __blk_mq_alloc_requests_batch(). Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx> --- block/blk-mq.c | 41 +++++++++++++++++++++++++++++++---------- block/blk-mq.h | 1 + include/linux/blk-mq.h | 6 +++--- 3 files changed, 35 insertions(+), 13 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index c50ef953759f..2849395ca4c6 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -337,6 +337,24 @@ void blk_rq_init(struct request_queue *q, struct request *rq) } EXPORT_SYMBOL(blk_rq_init); +/* Set alloc and start time when pre-allocated rq is actually used */ +static inline void blk_mq_rq_time_init(struct request *rq) +{ + if (blk_mq_need_time_stamp(rq->rq_flags)) { + u64 now = ktime_get_ns(); + +#ifdef CONFIG_BLK_RQ_ALLOC_TIME + /* + * The alloc time is only used by iocost for now, + * only possible when blk_mq_need_time_stamp(). + */ + if (blk_queue_rq_alloc_time(rq->q)) + rq->alloc_time_ns = now; +#endif + rq->start_time_ns = now; + } +} + static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data, struct blk_mq_tags *tags, unsigned int tag, u64 alloc_time_ns) { @@ -360,14 +378,11 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data, } rq->timeout = 0; - if (blk_mq_need_time_stamp(rq)) - rq->start_time_ns = ktime_get_ns(); - else - rq->start_time_ns = 0; rq->part = NULL; #ifdef CONFIG_BLK_RQ_ALLOC_TIME rq->alloc_time_ns = alloc_time_ns; #endif + rq->start_time_ns = data->start_time_ns; rq->io_start_time_ns = 0; rq->stats_sectors = 0; rq->nr_phys_segments = 0; @@ -397,8 +412,7 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data, } static inline struct request * -__blk_mq_alloc_requests_batch(struct blk_mq_alloc_data *data, - u64 alloc_time_ns) +__blk_mq_alloc_requests_batch(struct blk_mq_alloc_data *data) { unsigned int tag, tag_offset; struct blk_mq_tags *tags; @@ -417,7 +431,7 @@ __blk_mq_alloc_requests_batch(struct blk_mq_alloc_data *data, tag = tag_offset + i; prefetch(tags->static_rqs[tag]); tag_mask &= ~(1UL << i); - rq = blk_mq_rq_ctx_init(data, tags, tag, alloc_time_ns); + rq = blk_mq_rq_ctx_init(data, tags, tag, 0); rq_list_add(data->cached_rq, rq); nr++; } @@ -488,9 +502,11 @@ static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data) * Try batched alloc if we want more than 1 tag. */ if (data->nr_tags > 1) { - rq = __blk_mq_alloc_requests_batch(data, alloc_time_ns); - if (rq) + rq = __blk_mq_alloc_requests_batch(data); + if (rq) { + blk_mq_rq_time_init(rq); return rq; + } data->nr_tags = 1; } @@ -514,6 +530,9 @@ static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data) goto retry; } + if (blk_mq_need_time_stamp(data->rq_flags)) + data->start_time_ns = ktime_get_ns(); + return blk_mq_rq_ctx_init(data, blk_mq_tags_from_data(data), tag, alloc_time_ns); } @@ -570,6 +589,7 @@ static struct request *blk_mq_alloc_cached_request(struct request_queue *q, return NULL; plug->cached_rq = rq_list_next(rq); + blk_mq_rq_time_init(rq); } rq->cmd_flags = opf; @@ -1004,7 +1024,7 @@ static inline void __blk_mq_end_request_acct(struct request *rq, u64 now) inline void __blk_mq_end_request(struct request *rq, blk_status_t error) { - if (blk_mq_need_time_stamp(rq)) + if (blk_mq_need_time_stamp(rq->rq_flags)) __blk_mq_end_request_acct(rq, ktime_get_ns()); if (rq->end_io) { @@ -2891,6 +2911,7 @@ static inline struct request *blk_mq_get_cached_request(struct request_queue *q, plug->cached_rq = rq_list_next(rq); rq_qos_throttle(q, *bio); + blk_mq_rq_time_init(rq); rq->cmd_flags = (*bio)->bi_opf; INIT_LIST_HEAD(&rq->queuelist); return rq; diff --git a/block/blk-mq.h b/block/blk-mq.h index 1743857e0b01..29ed4d05110e 100644 --- a/block/blk-mq.h +++ b/block/blk-mq.h @@ -150,6 +150,7 @@ struct blk_mq_alloc_data { unsigned int shallow_depth; blk_opf_t cmd_flags; req_flags_t rq_flags; + u64 start_time_ns; /* allocate multiple requests/tags in one go */ unsigned int nr_tags; diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index f401067ac03a..e8366e9c3388 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -834,9 +834,9 @@ void blk_mq_end_request_batch(struct io_comp_batch *ib); * Only need start/end time stamping if we have iostat or * blk stats enabled, or using an IO scheduler. */ -static inline bool blk_mq_need_time_stamp(struct request *rq) +static inline bool blk_mq_need_time_stamp(req_flags_t rq_flags) { - return (rq->rq_flags & (RQF_IO_STAT | RQF_STATS | RQF_USE_SCHED)); + return (rq_flags & (RQF_IO_STAT | RQF_STATS | RQF_USE_SCHED)); } static inline bool blk_mq_is_reserved_rq(struct request *rq) @@ -860,7 +860,7 @@ static inline bool blk_mq_add_to_batch(struct request *req, iob->complete = complete; else if (iob->complete != complete) return false; - iob->need_ts |= blk_mq_need_time_stamp(req); + iob->need_ts |= blk_mq_need_time_stamp(req->rq_flags); rq_list_add(&iob->req_list, req); return true; } -- 2.39.2