diff mbox series

[-next,v3,1/2] blk-throttle: fix that io throttle can only work for single bio

Message ID 20220519085811.879097-2-yukuai3@huawei.com (mailing list archive)
State New, archived
Headers show
Series bugfix for blk-throttle | expand

Commit Message

Yu Kuai May 19, 2022, 8:58 a.m. UTC
commit 9f5ede3c01f9 ("block: throttle split bio in case of iops limit")
introduce a new problem, for example:

[root@localhost ~]# echo "8:0 1024" > /sys/fs/cgroup/blkio/blkio.throttle.write_bps_device
[root@localhost ~]# echo $$ > /sys/fs/cgroup/blkio/cgroup.procs
[root@localhost ~]# dd if=/dev/zero of=/dev/sda bs=10k count=1 oflag=direct &
[1] 620
[root@localhost ~]# dd if=/dev/zero of=/dev/sda bs=10k count=1 oflag=direct &
[2] 626
[root@localhost ~]# 1+0 records in
1+0 records out
10240 bytes (10 kB, 10 KiB) copied, 10.0038 s, 1.0 kB/s1+0 records in
1+0 records out

10240 bytes (10 kB, 10 KiB) copied, 9.23076 s, 1.1 kB/s
-> the second bio is issued after 10s instead of 20s.

This is because if some bios are already queued, current bio is queued
directly and the flag 'BIO_THROTTLED' is set. And later, when former
bios are dispatched, this bio will be dispatched without waiting at all,
this is due to tg_with_in_bps_limit() return 0 for this bio.

In order to fix the problem, don't skip flaged bio in
tg_with_in_bps_limit(), and for the problem that split bio can be
double accounted, compensate the over-accounting in __blk_throtl_bio().

Fixes: 9f5ede3c01f9 ("block: throttle split bio in case of iops limit")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/blk-throttle.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

Comments

Ming Lei May 19, 2022, 10:42 a.m. UTC | #1
On Thu, May 19, 2022 at 04:58:10PM +0800, Yu Kuai wrote:
> commit 9f5ede3c01f9 ("block: throttle split bio in case of iops limit")
> introduce a new problem, for example:
> 
> [root@localhost ~]# echo "8:0 1024" > /sys/fs/cgroup/blkio/blkio.throttle.write_bps_device
> [root@localhost ~]# echo $$ > /sys/fs/cgroup/blkio/cgroup.procs
> [root@localhost ~]# dd if=/dev/zero of=/dev/sda bs=10k count=1 oflag=direct &
> [1] 620
> [root@localhost ~]# dd if=/dev/zero of=/dev/sda bs=10k count=1 oflag=direct &
> [2] 626
> [root@localhost ~]# 1+0 records in
> 1+0 records out
> 10240 bytes (10 kB, 10 KiB) copied, 10.0038 s, 1.0 kB/s1+0 records in
> 1+0 records out
> 
> 10240 bytes (10 kB, 10 KiB) copied, 9.23076 s, 1.1 kB/s
> -> the second bio is issued after 10s instead of 20s.
> 
> This is because if some bios are already queued, current bio is queued
> directly and the flag 'BIO_THROTTLED' is set. And later, when former
> bios are dispatched, this bio will be dispatched without waiting at all,
> this is due to tg_with_in_bps_limit() return 0 for this bio.
> 
> In order to fix the problem, don't skip flaged bio in
> tg_with_in_bps_limit(), and for the problem that split bio can be
> double accounted, compensate the over-accounting in __blk_throtl_bio().
> 
> Fixes: 9f5ede3c01f9 ("block: throttle split bio in case of iops limit")
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Thanks,
Ming
diff mbox series

Patch

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 447e1b8722f7..0c37be08ff28 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -811,7 +811,7 @@  static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
 	unsigned int bio_size = throtl_bio_data_size(bio);
 
 	/* no need to throttle if this bio's bytes have been accounted */
-	if (bps_limit == U64_MAX || bio_flagged(bio, BIO_THROTTLED)) {
+	if (bps_limit == U64_MAX) {
 		if (wait)
 			*wait = 0;
 		return true;
@@ -921,11 +921,8 @@  static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
 	unsigned int bio_size = throtl_bio_data_size(bio);
 
 	/* Charge the bio to the group */
-	if (!bio_flagged(bio, BIO_THROTTLED)) {
-		tg->bytes_disp[rw] += bio_size;
-		tg->last_bytes_disp[rw] += bio_size;
-	}
-
+	tg->bytes_disp[rw] += bio_size;
+	tg->last_bytes_disp[rw] += bio_size;
 	tg->io_disp[rw]++;
 	tg->last_io_disp[rw]++;
 
@@ -2121,6 +2118,21 @@  bool __blk_throtl_bio(struct bio *bio)
 			tg->last_low_overflow_time[rw] = jiffies;
 		throtl_downgrade_check(tg);
 		throtl_upgrade_check(tg);
+
+		/*
+		 * re-entered bio has accounted bytes already, so try to
+		 * compensate previous over-accounting. However, if new
+		 * slice is started, just forget it.
+		 */
+		if (bio_flagged(bio, BIO_THROTTLED)) {
+			unsigned int bio_size = throtl_bio_data_size(bio);
+
+			if (tg->bytes_disp[rw] >= bio_size)
+				tg->bytes_disp[rw] -= bio_size;
+			if (tg->last_bytes_disp[rw] >= bio_size)
+				tg->last_bytes_disp[rw] -= bio_size;
+		}
+
 		/* throtl is FIFO - if bios are already queued, should queue */
 		if (sq->nr_queued[rw])
 			break;