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

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Date:   Tue, 23 Aug 2022 08:08:43 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     axboe@...nel.dk, ming.lei@...hat.com, mkoutny@...e.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, yukuai3@...wei.com, yi.zhang@...wei.com
Subject: Re: [PATCH v8 4/4] blk-throttle: fix io hung due to configuration
 updates

On Tue, Aug 23, 2022 at 11:31:30AM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@...wei.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@...wei.com>

For 2-4,

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

Thanks.

-- 
tejun