From: Pavel Begunkov <[email protected]> Commit 4bc6339a583cec650b05 ("block: move blk_stat_add() to __blk_mq_end_request()") moved blk_stat_add(), so now it's called after blk_update_request(), which zeroes rq->__data_len. Without length, blk_stat_add() can't calculate stat bucket and returns error, effectively disabling hybrid polling.
__blk_mq_end_request() is a right place to call blk_stat_add(), as it's guaranteed to be called for each request. Yet, calculating time there won't provide sufficient accuracy/precision for finer tuned hybrid polling, because a path from __blk_mq_complete_request() to __blk_mq_end_request() adds unpredictable overhead. Add io_end_time_ns field in struct request, save time as soon as possible (at __blk_mq_complete_request()) and reuse later. Signed-off-by: Pavel Begunkov <[email protected]> --- block/blk-mq.c | 13 ++++++++++--- block/blk-stat.c | 4 ++-- block/blk-stat.h | 2 +- include/linux/blkdev.h | 11 +++++++++++ 4 files changed, 24 insertions(+), 6 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index 32b8ad3d341b..8f6b6bfe0ccb 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -330,6 +330,7 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data, else rq->start_time_ns = 0; rq->io_start_time_ns = 0; + rq->io_end_time_ns = 0; rq->nr_phys_segments = 0; #if defined(CONFIG_BLK_DEV_INTEGRITY) rq->nr_integrity_segments = 0; @@ -532,14 +533,17 @@ EXPORT_SYMBOL_GPL(blk_mq_free_request); inline void __blk_mq_end_request(struct request *rq, blk_status_t error) { - u64 now = 0; + u64 now = rq->io_end_time_ns; - if (blk_mq_need_time_stamp(rq)) + /* called directly bypassing __blk_mq_complete_request */ + if (blk_mq_need_time_stamp(rq) && !now) { now = ktime_get_ns(); + rq->io_end_time_ns = now; + } if (rq->rq_flags & RQF_STATS) { blk_mq_poll_stats_start(rq->q); - blk_stat_add(rq, now); + blk_stat_add(rq); } if (rq->internal_tag != -1) @@ -579,6 +583,9 @@ static void __blk_mq_complete_request(struct request *rq) bool shared = false; int cpu; + if (blk_mq_need_time_stamp(rq)) + rq->io_end_time_ns = ktime_get_ns(); + WRITE_ONCE(rq->state, MQ_RQ_COMPLETE); /* * Most of single queue controllers, there is only one irq vector diff --git a/block/blk-stat.c b/block/blk-stat.c index 940f15d600f8..9b9b30927ea8 100644 --- a/block/blk-stat.c +++ b/block/blk-stat.c @@ -48,7 +48,7 @@ void blk_rq_stat_add(struct blk_rq_stat *stat, u64 value) stat->nr_samples++; } -void blk_stat_add(struct request *rq, u64 now) +void blk_stat_add(struct request *rq) { struct request_queue *q = rq->q; struct blk_stat_callback *cb; @@ -56,7 +56,7 @@ void blk_stat_add(struct request *rq, u64 now) int bucket; u64 value; - value = (now >= rq->io_start_time_ns) ? now - rq->io_start_time_ns : 0; + value = blk_rq_io_time(rq); blk_throtl_stat_add(rq, value); diff --git a/block/blk-stat.h b/block/blk-stat.h index 17b47a86eefb..2653818cee36 100644 --- a/block/blk-stat.h +++ b/block/blk-stat.h @@ -65,7 +65,7 @@ struct blk_stat_callback { struct blk_queue_stats *blk_alloc_queue_stats(void); void blk_free_queue_stats(struct blk_queue_stats *); -void blk_stat_add(struct request *rq, u64 now); +void blk_stat_add(struct request *rq); /* record time/size info in request but not add a callback */ void blk_stat_enable_accounting(struct request_queue *q); diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 592669bcc536..2a8d4b68d707 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -198,6 +198,9 @@ struct request { u64 start_time_ns; /* Time that I/O was submitted to the device. */ u64 io_start_time_ns; + /* Time that I/O was reported completed by the device. */ + u64 io_end_time_ns; + #ifdef CONFIG_BLK_WBT unsigned short wbt_flags; @@ -385,6 +388,14 @@ static inline int blkdev_reset_zones_ioctl(struct block_device *bdev, #endif /* CONFIG_BLK_DEV_ZONED */ +static inline u64 blk_rq_io_time(struct request *rq) +{ + u64 start = rq->io_start_time_ns; + u64 end = rq->io_end_time_ns; + + return (end - start) ? end - start : 0; +} + struct request_queue { /* * Together with queue_head for cacheline sharing -- 2.21.0
