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