[PATCH v3] block: propagate in_flight to whole disk on partition I/O
From: Tang Yizhou <hidden>
Date: 2026-05-22 13:14:17
Also in:
lkml
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, Linus Torvalds
From: Tang Yizhou <redacted>
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")
v2: Update commit message.
v3: Take Christoph's advice and factor the common code into two helpers.
Suggested-by: Leon Hwang <redacted>
Signed-off-by: Tang Yizhou <redacted>
---
block/blk-core.c | 4 ++--
block/blk-mq.c | 5 ++---
block/blk.h | 22 ++++++++++++++++++++++
3 files changed, 26 insertions(+), 5 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index 17450058ea6d..81b322b8a385 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c@@ -1042,7 +1042,7 @@ 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)]); + bdev_inc_in_flight(bdev, op); part_stat_unlock(); return start_time;
@@ -1073,7 +1073,7 @@ void bdev_end_io_acct(struct block_device *bdev, enum req_op op, part_stat_inc(bdev, ios[sgrp]); 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)]); + bdev_inc_in_flight(bdev, op); part_stat_unlock(); } EXPORT_SYMBOL(bdev_end_io_acct);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index d0c37daf568f..6bdfe642bd93 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c@@ -1082,8 +1082,7 @@ static inline void blk_account_io_done(struct request *req, u64 now) update_io_ticks(req->part, jiffies, true); part_stat_inc(req->part, ios[sgrp]); 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))]); + bdev_dec_in_flight(req->part, req_op(req)); part_stat_unlock(); } }
@@ -1143,7 +1142,7 @@ 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))]); + bdev_inc_in_flight(req->part, req_op(req)); part_stat_unlock(); }
diff --git a/block/blk.h b/block/blk.h
index b998a7761faf..05099aab6863 100644
--- a/block/blk.h
+++ b/block/blk.h@@ -4,6 +4,7 @@ #include <linux/bio-integrity.h> #include <linux/blk-crypto.h> +#include <linux/part_stat.h> #include <linux/lockdep.h> #include <linux/memblock.h> /* for max_pfn/max_low_pfn */ #include <linux/sched/sysctl.h>
@@ -11,6 +12,7 @@ #include <xen/xen.h> #include "blk-crypto-internal.h" + struct elv_change_ctx; /*
@@ -485,6 +487,26 @@ static inline void req_set_nomerge(struct request_queue *q, struct request *req) q->last_merge = NULL; } +static inline void bdev_inc_in_flight(struct block_device *bdev, + enum req_op op) +{ + bool rw = op_is_write(op); + + part_stat_local_inc(bdev, in_flight[rw]); + if (bdev_is_partition(bdev)) + part_stat_local_inc(bdev_whole(bdev), in_flight[rw]); +} + +static inline void bdev_dec_in_flight(struct block_device *bdev, + enum req_op op) +{ + bool rw = op_is_write(op); + + part_stat_local_dec(bdev, in_flight[rw]); + if (bdev_is_partition(bdev)) + part_stat_local_dec(bdev_whole(bdev), in_flight[rw]); +} + /* * Internal io_context interface */
--
2.43.0