On 5/28/2019 9:37 PM, Omar Sandoval wrote: > On Sat, May 25, 2019 at 04:42:11PM +0300, Pavel Begunkov (Silence) wrote: >> 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. > > I don't see how this patch fixes this problem, am I missing something? > The timing issue seems orthogonal. You're right, it got completely mixed up. It's rather an addition to a patch from Hou Tao. But considering your comment below, it would be better just to revert part of changes.
> >> __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; > > Kyber expects the timestamp passed in to kyber_complete_request() to > include the software overhead. iostat should probably include the > software overhead, too. So, we probably won't be able to avoid calling > ktime_get() twice, once for I/O time and one for the end-to-end time. I asked that in another thread, and it seems we can't reuse this. > >> - 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; > > I think you meant: > > return end >= start ? end - start : 0; > Sure, thanks >> +} >> + >> struct request_queue { >> /* >> * Together with queue_head for cacheline sharing >> -- >> 2.21.0 >>
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