I mean this way https://lore.kernel.org/linux-block/dd30f4d94aa19956ad4500b1177741fd071ec37f.1558791181.git.asml.silence@xxxxxxxxx/T/#u On 25/05/2019 14:46, Pavel Begunkov wrote: > That's the same bug I posted a patch about 3+ weeks ago. No answer yet, > however. > https://www.spinics.net/lists/linux-block/msg40049.html > > I think putting time sampling at __blk_mq_end_request() won't give > sufficient precision for more sophisticated hybrid polling, because path > __blk_mq_complete_request() -> __blk_mq_end_request() adds a lot of > overhead (redirect rq to another cpu, dma unmap, etc). That's the case > for mentioned patchset > https://www.spinics.net/lists/linux-block/msg40044.html > > It works OK for 50-80us requests (e.g. SSD read), but is not good enough > for 20us and less (e.g. SSD write). I think it would be better to save > the time in advance, and use it later. > > By the way, it seems, that __blk_mq_end_request() is really better place > to record stats, as not all drivers use __blk_mq_complete_request(), > even though they don't implement blk_poll(). > > > On 21/05/2019 10:59, Hou Tao wrote: >> Currently rq->data_len will be decreased by partial completion or >> zeroed by completion, so when blk_stat_add() is invoked, data_len >> will be zero and there will never be samples in poll_cb because >> blk_mq_poll_stats_bkt() will return -1 if data_len is zero. >> >> We could move blk_stat_add() back to __blk_mq_complete_request(), >> but that would make the effort of trying to call ktime_get_ns() >> once in vain. Instead we can reuse throtl_size field, and use >> it for both block stats and block throttle, and adjust the >> logic in blk_mq_poll_stats_bkt() accordingly. >> >> Fixes: 4bc6339a583c ("block: move blk_stat_add() to __blk_mq_end_request()") >> Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx> >> --- >> block/blk-mq.c | 11 +++++------ >> block/blk-throttle.c | 3 ++- >> include/linux/blkdev.h | 15 ++++++++++++--- >> 3 files changed, 19 insertions(+), 10 deletions(-) >> >> diff --git a/block/blk-mq.c b/block/blk-mq.c >> index 08a6248d8536..4d1462172f0f 100644 >> --- a/block/blk-mq.c >> +++ b/block/blk-mq.c >> @@ -44,12 +44,12 @@ static void blk_mq_poll_stats_fn(struct blk_stat_callback *cb); >> >> static int blk_mq_poll_stats_bkt(const struct request *rq) >> { >> - int ddir, bytes, bucket; >> + int ddir, sectors, bucket; >> >> ddir = rq_data_dir(rq); >> - bytes = blk_rq_bytes(rq); >> + sectors = blk_rq_stats_sectors(rq); >> >> - bucket = ddir + 2*(ilog2(bytes) - 9); >> + bucket = ddir + 2 * ilog2(sectors); >> >> if (bucket < 0) >> return -1; >> @@ -329,6 +329,7 @@ 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->stats_sectors = 0; >> rq->nr_phys_segments = 0; >> #if defined(CONFIG_BLK_DEV_INTEGRITY) >> rq->nr_integrity_segments = 0; >> @@ -678,9 +679,7 @@ void blk_mq_start_request(struct request *rq) >> >> if (test_bit(QUEUE_FLAG_STATS, &q->queue_flags)) { >> rq->io_start_time_ns = ktime_get_ns(); >> -#ifdef CONFIG_BLK_DEV_THROTTLING_LOW >> - rq->throtl_size = blk_rq_sectors(rq); >> -#endif >> + rq->stats_sectors = blk_rq_sectors(rq); >> rq->rq_flags |= RQF_STATS; >> rq_qos_issue(q, rq); >> } >> diff --git a/block/blk-throttle.c b/block/blk-throttle.c >> index 1b97a73d2fb1..88459a4ac704 100644 >> --- a/block/blk-throttle.c >> +++ b/block/blk-throttle.c >> @@ -2249,7 +2249,8 @@ void blk_throtl_stat_add(struct request *rq, u64 time_ns) >> struct request_queue *q = rq->q; >> struct throtl_data *td = q->td; >> >> - throtl_track_latency(td, rq->throtl_size, req_op(rq), time_ns >> 10); >> + throtl_track_latency(td, blk_rq_stats_sectors(rq), req_op(rq), >> + time_ns >> 10); >> } >> >> void blk_throtl_bio_endio(struct bio *bio) >> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h >> index 1aafeb923e7b..68a0841d3554 100644 >> --- a/include/linux/blkdev.h >> +++ b/include/linux/blkdev.h >> @@ -202,9 +202,12 @@ struct request { >> #ifdef CONFIG_BLK_WBT >> unsigned short wbt_flags; >> #endif >> -#ifdef CONFIG_BLK_DEV_THROTTLING_LOW >> - unsigned short throtl_size; >> -#endif >> + /* >> + * rq sectors used for blk stats. It has the same value >> + * with blk_rq_sectors(rq), except that it never be zeroed >> + * by completion. >> + */ >> + unsigned short stats_sectors; >> >> /* >> * Number of scatter-gather DMA addr+len pairs after >> @@ -892,6 +895,7 @@ static inline struct request_queue *bdev_get_queue(struct block_device *bdev) >> * blk_rq_err_bytes() : bytes left till the next error boundary >> * blk_rq_sectors() : sectors left in the entire request >> * blk_rq_cur_sectors() : sectors left in the current segment >> + * blk_rq_stats_sectors() : sectors of the entire request used for stats >> */ >> static inline sector_t blk_rq_pos(const struct request *rq) >> { >> @@ -920,6 +924,11 @@ static inline unsigned int blk_rq_cur_sectors(const struct request *rq) >> return blk_rq_cur_bytes(rq) >> SECTOR_SHIFT; >> } >> >> +static inline unsigned int blk_rq_stats_sectors(const struct request *rq) >> +{ >> + return rq->stats_sectors; >> +} >> + >> #ifdef CONFIG_BLK_DEV_ZONED >> static inline unsigned int blk_rq_zone_no(struct request *rq) >> { >> > -- Yours sincerely, Pavel Begunkov
Attachment:
signature.asc
Description: OpenPGP digital signature
