[PATCH v5] block: propagate in_flight to whole disk on partition I/O

[PATCH v5] block: propagate in_flight to whole disk on partition I/O

[Tang Yizhou]

From: Tang Yizhou <yizhou.tang@shopee.com>

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 <leon.huangfu@shopee.com>
Signed-off-by: Tang Yizhou <yizhou.tang@shopee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
v2: Update commit message.
v3: Take Christoph's advice and factor the common code into two helpers.
v4: Remove my redundant new line in blk.h. Add Christoph's Reviewed-by
tag.
v5: Remove the changelog from the commit message.
 block/blk-core.c |  4 ++--
 block/blk-mq.c   |  5 ++---
 block/blk.h      | 21 +++++++++++++++++++++
 3 files changed, 25 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..11245a494c43 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>
@@ -485,6 +486,26 @@ 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

Re: [PATCH v5] block: propagate in_flight to whole disk on partition I/O

[Keith Busch]

On Fri, May 22, 2026 at 10:16:38PM +0800, Tang Yizhou wrote:
> @@ -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);

This one should be bdev_dec_in_flight().

Re: [PATCH v5] block: propagate in_flight to whole disk on partition I/O

[Jens Axboe]

On 5/22/26 8:24 AM, Keith Busch wrote:
> On Fri, May 22, 2026 at 10:16:38PM +0800, Tang Yizhou wrote:
>> @@ -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);
> 
> This one should be bdev_dec_in_flight().

Yes, and let's chill the repostings. Send 1 per day, we've up to v5 in a
very short amount of time. Take your time and get it right, and give
people a chance to comment and review before randomly throwing version
N+1 over the wall.

-- 
Jens Axboe

Re: [PATCH v5] block: propagate in_flight to whole disk on partition I/O

[Yizhou Tang]

On Fri, May 22, 2026 at 10:53 PM Keith Busch <kbusch@kernel.org> wrote:
>
> On Fri, May 22, 2026 at 10:16:38PM +0800, Tang Yizhou wrote:
> > @@ -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);
>
> This one should be bdev_dec_in_flight().

Thanks for pointing that out.

Best regards,
Yi

>