From 5c17f45e91f5035c1b317e93b3dfb01088ac2902 Mon Sep 17 00:00:00 2001 From: Chengming Zhou Date: Mon, 10 Jul 2023 18:55:16 +0800 Subject: blk-mq: fix start_time_ns and alloc_time_ns for pre-allocated rq 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(). Fix it by setting alloc_time_ns and start_time_ns to now when the allocated request is actually used. Signed-off-by: Chengming Zhou Acked-by: Tejun Heo Reviewed-by: Christoph Hellwig Link: https://lore.kernel.org/r/20230710105516.2053478-1-chengming.zhou@linux.dev Signed-off-by: Jens Axboe --- block/blk-mq.c | 47 ++++++++++++++++++++++++++++++----------------- 1 file changed, 30 insertions(+), 17 deletions(-) (limited to 'block/blk-mq.c') diff --git a/block/blk-mq.c b/block/blk-mq.c index 5504719b970d..d50b1d62a3d9 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -328,8 +328,24 @@ void blk_rq_init(struct request_queue *q, struct request *rq) } EXPORT_SYMBOL(blk_rq_init); +/* Set start and alloc time when the allocated request is actually used */ +static inline void blk_mq_rq_time_init(struct request *rq, u64 alloc_time_ns) +{ + if (blk_mq_need_time_stamp(rq)) + rq->start_time_ns = ktime_get_ns(); + else + rq->start_time_ns = 0; + +#ifdef CONFIG_BLK_RQ_ALLOC_TIME + if (blk_queue_rq_alloc_time(rq->q)) + rq->alloc_time_ns = alloc_time_ns ?: rq->start_time_ns; + else + rq->alloc_time_ns = 0; +#endif +} + 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) + struct blk_mq_tags *tags, unsigned int tag) { struct blk_mq_ctx *ctx = data->ctx; struct blk_mq_hw_ctx *hctx = data->hctx; @@ -356,14 +372,7 @@ 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->io_start_time_ns = 0; rq->stats_sectors = 0; rq->nr_phys_segments = 0; @@ -393,8 +402,7 @@ 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; @@ -413,7 +421,7 @@ __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); rq_list_add(data->cached_rq, rq); nr++; } @@ -474,9 +482,11 @@ retry: * 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, alloc_time_ns); return rq; + } data->nr_tags = 1; } @@ -499,8 +509,9 @@ retry: goto retry; } - return blk_mq_rq_ctx_init(data, blk_mq_tags_from_data(data), tag, - alloc_time_ns); + rq = blk_mq_rq_ctx_init(data, blk_mq_tags_from_data(data), tag); + blk_mq_rq_time_init(rq, alloc_time_ns); + return rq; } static struct request *blk_mq_rq_cache_fill(struct request_queue *q, @@ -555,6 +566,7 @@ 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, 0); } rq->cmd_flags = opf; @@ -656,8 +668,8 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q, tag = blk_mq_get_tag(&data); if (tag == BLK_MQ_NO_TAG) goto out_queue_exit; - rq = blk_mq_rq_ctx_init(&data, blk_mq_tags_from_data(&data), tag, - alloc_time_ns); + rq = blk_mq_rq_ctx_init(&data, blk_mq_tags_from_data(&data), tag); + blk_mq_rq_time_init(rq, alloc_time_ns); rq->__data_len = 0; rq->__sector = (sector_t) -1; rq->bio = rq->biotail = NULL; @@ -2896,6 +2908,7 @@ 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, 0); rq->cmd_flags = (*bio)->bi_opf; INIT_LIST_HEAD(&rq->queuelist); return rq; -- cgit