linux-kernel - Re: [PATCH v2] blk-throttle: Fix io statistics for cgroup v1

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Date:   Mon, 3 Apr 2023 17:30:21 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Jinke Han <hanjinke.666@...edance.com>
Cc:     tj@...nel.org, josef@...icpanda.com, axboe@...nel.dk,
        cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] blk-throttle: Fix io statistics for cgroup v1

On Sat, Apr 01, 2023 at 05:47:08PM +0800, Jinke Han <hanjinke.666@...edance.com> wrote:
> From: Jinke Han <hanjinke.666@...edance.com>
> 
> After commit f382fb0bcef4 ("block: remove legacy IO schedulers"),
> blkio.throttle.io_serviced and blkio.throttle.io_service_bytes become
> the only stable io stats interface of cgroup v1,

There is also blkio.bfq.{io_serviced,io_service_bytes} couple, so it's
not the only. Or do you mean stable in terms of used IO scheduler?

> and these statistics are done in the blk-throttle code. But the
> current code only counts the bios that are actually throttled. When
> the user does not add the throttle limit,

... "or the limit doesn't kick in"

> the io stats for cgroup v1 has nothing.


> I fix it according to the statistical method of v2, and made it count
> all ios accurately.

s/all ios/all bios and split ios/ 

(IIUC you fix two things)

> Fixes: a7b36ee6ba29 ("block: move blk-throtl fast path inline")

Good catch.

Does it also undo the performance gain from that commit? (Or rather,
have you observed effect of your patch on v2-only performance?)

> Signed-off-by: Jinke Han <hanjinke.666@...edance.com>
> ---
>  block/blk-cgroup.c   | 6 ++++--
>  block/blk-throttle.c | 6 ------
>  block/blk-throttle.h | 9 +++++++++
>  3 files changed, 13 insertions(+), 8 deletions(-)

The code looks correct.

Thanks,
Michal

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