From: Tao Cui <cui.tao@linux.dev>
To: bot+bpf-ci@kernel.org, tj@kernel.org, josef@toxicopanda.com,
axboe@kernel.dk, alexei.starovoitov@gmail.com
Cc: cui.tao@linux.dev, cgroups@vger.kernel.org,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
bpf@vger.kernel.org, andrii@kernel.org, eddyz87@gmail.com,
ast@kernel.org, daniel@iogearbox.net,
linux-kselftest@vger.kernel.org, cuitao@kylinos.cn,
ameryhung@gmail.com, martin.lau@kernel.org,
yonghong.song@linux.dev, mason@kernel.org,
ihor.solodrai@linux.dev
Subject: Re: [RFC PATCH v13 2/4] blk-iocost: add iocost_ioc_tick tracepoint for per-period device summary
Date: Mon, 9 Nov 2026 21:05:53 +0800 [thread overview]
Message-ID: <1c4078e4-dd6a-4a70-bdda-d5cded19937a@linux.dev> (raw)
In-Reply-To: <ebb6ebc5ddce3089fe912ca2d6e7a0658864c7369d15e1cdb7f203eae6d5a0d0@mail.kernel.org>
Hello,
在 2026/11/6 20:56, bot+bpf-ci@kernel.org 写道:
>> blk-iocost: add iocost_ioc_tick tracepoint for per-period device summary
>
> TL;DR: Commit message only: it restates the code comment instead of giving the
> motivation (monitoring without drgn) for the new iocost_ioc_tick tracepoint.
Right, the changelog ended up restating the code comment. I'll
rewrite it to lead with the motivation: the tracepoint gives a
per-period summary so monitoring iocost doesn't require drgn. The
emission semantics stay documented in the code.
Thanks,
Tao
> Not a bug.
>
>> blk-iocost: add iocost_ioc_tick tracepoint for per-period device summary
>>
>> Add iocost_ioc_tick, emitted once per period from ioc_timer_fn() with
>> the overall controller state: period_us, vrate, busy_level, active iocg
>> count and usage percentage. busy_level, cur_period, nr_active and
>> usage_us_sum are complete at the emission point. usage is wall time
>> over wall time, summed over iocgs, and is not capped at 100. vrate and
>> period_us reflect the current controller state, which an io.cost.qos
>> write may have changed mid-period.
>>
>> The event fires every period the controller is running, including
>> steady states, plus one final tick before the controller goes idle, so
>> the transition to dormancy is directly visible. The active iocg count
>> is only gathered when the tracepoint is enabled.
>>
>> Suggested-by: Tejun Heo <tj@kernel.org>
>> Signed-off-by: Tao Cui <cuitao@kylinos.cn>
>
> this isn't a bug, but the middle of the first paragraph ("busy_level,
> cur_period, nr_active and usage_us_sum are complete at the emission point
> ... which an io.cost.qos write may have changed mid-period") restates the
> block comment added above the tracepoint call in ioc_timer_fn() almost word
> for word.
>
> The reason for adding the event only appears in the comment in
> include/trace/events/iocost.h ("so basic monitoring doesn't require drgn").
>
> Could the changelog say why a per-period summary event is needed, for
> example the monitoring-without-drgn motivation, rather than repeating the
> code comment?
>
>
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
>
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/42219005018
next prev parent reply other threads:[~2026-11-09 13:06 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-06 12:23 [RFC PATCH v13 0/4] blk-iocost: BPF struct_ops cost model Tao Cui
2026-11-06 12:23 ` [RFC PATCH v13 1/4] blk-iocost: add BPF struct_ops cost model support Tao Cui
2026-11-06 12:23 ` [RFC PATCH v13 2/4] blk-iocost: add iocost_ioc_tick tracepoint for per-period device summary Tao Cui
2026-11-06 12:56 ` bot+bpf-ci
2026-11-09 13:05 ` Tao Cui [this message]
2026-11-06 12:23 ` [RFC PATCH v13 3/4] selftests/bpf: add iocost cost model test Tao Cui
2026-11-06 12:56 ` bot+bpf-ci
2026-11-06 12:23 ` [RFC PATCH v13 4/4] docs: cgroup-v2: document the iocost BPF cost model attachment Tao Cui
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