linux-kernel - Re: [PATCH 13/13] blk: introduce iostat per cgroup module

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Date:   Wed, 12 Jan 2022 10:13:40 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Wang Jianchao <jianchao.wan9@...il.com>
Cc:     axboe@...nel.dk, jbacik@...com, bvanassche@....org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/13] blk: introduce iostat per cgroup module

On Mon, Jan 10, 2022 at 05:10:46PM +0800, Wang Jianchao wrote:
> From: Wang Jianchao <wangjianchao@...ishou.com>
> 
> iostat can only track the whole device's io statistics. This patch
> introduces iostat per cgroup based on blk-rq-qos framework which
> can track bw, iops, queue latency and device latency and distinguish
> regular or meta data. The blkio.iostat per cgroup output in following
> format,
> vda-data bytes iops queue_lat dev_lat [ditto]  [ditto]
>     meta   \___________ ______________/    |        |
> 	               v                   v        v
> 	             read               write   discard
> In particular, the blkio.iostat of root only output the statistics
> of IOs from root cgroup. However, the non-root blkio.iostat outputs
> all of the children cgroups. With meta stats in root cgroup, hope
> to observe the performace of fs metadata.

I think using bpf is a way better solution for this kind of detailed
statistics. What if I want to know what portions are random, or the
distribution of IO sizes? Do I add another rq-qos policy or add another
interface file with interface versioning?

Thanks.

-- 
tejun