From: Tang Yizhou Now when I/O is submitted to a partition, the per-CPU in_flight[] counter is incremented only on the partition's block_device, not on the underlying whole disk. This leads to a problem which can be shown by a fio test: lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS mydev 252:1 0 20G 0 disk └─mydev1 259:0 0 10G 0 part iostat -xp 1 Device r/s rkB/s ... aqu-sz %util mydev 128153.00 512612.00 ... 13.22 72.20 mydev1 128154.00 512616.00 ... 13.22 100.00 %util is different between mydev and mydev1, which is unexpected. This is the cumulative effect of a series of patches. The root cause is commit e016b78201a2 ("block: return just one value from part_in_flight"), which deleted the branch in part_in_flight() that aggregated the whole-disk in_flight count on top of the partition's. Then the second commit is commit 10ec5e86f9b8 ("block: merge part_{inc,dev}_in_flight into their only callers"), which folded the whole-disk in_flight accounting into generic_start_io_acct() and generic_end_io_acct(). Those two helpers were then removed by commit e722fff238bb ("block: remove generic_{start,end}_io_acct"), and from that point on the whole disk's in_flight is no longer accounted at all. In update_io_ticks(), if calling bdev_count_inflight() finds that the inflight value of the whole device is 0, the accumulation of io_ticks will be skipped, causing the reported util% value to be underestimated. Fix it by restoring the whole-disk in_flight accounting. Fixes: e016b78201a2 ("block: return just one value from part_in_flight") Suggested-by: Leon Hwang Signed-off-by: Tang Yizhou --- v2: Update commit message. block/blk-core.c | 4 ++++ block/blk-mq.c | 6 ++++++ 2 files changed, 10 insertions(+) diff --git a/block/blk-core.c b/block/blk-core.c index 17450058ea6d..03f4b7015e69 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -1043,6 +1043,8 @@ unsigned long bdev_start_io_acct(struct block_device *bdev, enum req_op op, part_stat_lock(); update_io_ticks(bdev, start_time, false); part_stat_local_inc(bdev, in_flight[op_is_write(op)]); + if (bdev_is_partition(bdev)) + part_stat_local_inc(bdev_whole(bdev), in_flight[op_is_write(op)]); part_stat_unlock(); return start_time; @@ -1074,6 +1076,8 @@ void bdev_end_io_acct(struct block_device *bdev, enum req_op op, part_stat_add(bdev, sectors[sgrp], sectors); part_stat_add(bdev, nsecs[sgrp], jiffies_to_nsecs(duration)); part_stat_local_dec(bdev, in_flight[op_is_write(op)]); + if (bdev_is_partition(bdev)) + part_stat_local_dec(bdev_whole(bdev), in_flight[op_is_write(op)]); part_stat_unlock(); } EXPORT_SYMBOL(bdev_end_io_acct); diff --git a/block/blk-mq.c b/block/blk-mq.c index d0c37daf568f..60ead16f1496 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1084,6 +1084,9 @@ static inline void blk_account_io_done(struct request *req, u64 now) part_stat_add(req->part, nsecs[sgrp], now - req->start_time_ns); part_stat_local_dec(req->part, in_flight[op_is_write(req_op(req))]); + if (bdev_is_partition(req->part)) + part_stat_local_dec(bdev_whole(req->part), + in_flight[op_is_write(req_op(req))]); part_stat_unlock(); } } @@ -1144,6 +1147,9 @@ static inline void blk_account_io_start(struct request *req) part_stat_lock(); update_io_ticks(req->part, jiffies, false); part_stat_local_inc(req->part, in_flight[op_is_write(req_op(req))]); + if (bdev_is_partition(req->part)) + part_stat_local_inc(bdev_whole(req->part), + in_flight[op_is_write(req_op(req))]); part_stat_unlock(); } -- 2.43.0