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. > __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. > - 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; > +} > + > struct request_queue { > /* > * Together with queue_head for cacheline sharing > -- > 2.21.0 >
