Re: [PATCH v8 4/4] blk-throttle: fix io hung due to configuration updates

Tejun Heo
2022-08-23T18:08:43Z

On Tue, Aug 23, 2022 at 11:31:30AM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
>
> If new configuration is submitted while a bio is throttled, then new
> waiting time is recalculated regardless that the bio might already wait
> for some time:
>
> tg_conf_updated
> throtl_start_new_slice
> tg_update_disptime
> throtl_schedule_next_dispatch
>
> Then io hung can be triggered by always submmiting new configuration
> before the throttled bio is dispatched.
>
> Fix the problem by respecting the time that throttled bio already waited.
> In order to do that, add new fields to record how many bytes/io are
> waited, and use it to calculate wait time for throttled bio under new
> configuration.
>
> Some simple test:
> 1)
> cd /sys/fs/cgroup/blkio/
> echo $$ > cgroup.procs
> echo "8:0 2048" > blkio.throttle.write_bps_device
> {
> sleep 2
> echo "8:0 1024" > blkio.throttle.write_bps_device
> } &
> dd if=/dev/zero of=/dev/sda bs=8k count=1 oflag=direct
>
> 2)
> cd /sys/fs/cgroup/blkio/
> echo $$ > cgroup.procs
> echo "8:0 1024" > blkio.throttle.write_bps_device
> {
> sleep 4
> echo "8:0 2048" > blkio.throttle.write_bps_device
> } &
> dd if=/dev/zero of=/dev/sda bs=8k count=1 oflag=direct
>
> test results: io finish time
> before this patch with this patch
> 1) 10s 6s
> 2) 8s 6s
>
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>

For 2-4,

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

--
tejun