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

[Tejun Heo <tj@kernel.org>]

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