linux-kernel - Re: [PATCH 3/3] schedutil: trace: Add tracing to capture filter out requests

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Date:   Mon, 3 Apr 2023 18:02:17 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Qais Yousef <qyousef@...alina.io>
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        rostedt@...dmis.org, mhiramat@...nel.org, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vschneid@...hat.com, delyank@...com, qyousef@...gle.com
Subject: Re: [PATCH 3/3] schedutil: trace: Add tracing to capture filter out
 requests



On 4/3/23 14:46, Qais Yousef wrote:
> On 03/22/23 15:18, Lukasz Luba wrote:
>> Some of the frequency update requests coming form the task scheduler
>> might be filter out. It can happen when the previous request was served
>> not that long ago (in a period smaller than provided by the cpufreq driver
>> as minimum for frequency update). In such case, we want to know if some of
>> the frequency updates cannot make through.
>> Export the new tracepoint as well. That would allow to handle it by a
>> toolkit for trace analyzes.
> 
> I think you can use register_kretprobe() for this one. When functions are not
> inlined it should be easy to hook into them and you can get the return value of
> the function too.

Could be possible, but that's a different pattern to what we have in
terms of LISa. It's also a bit complicated for downstream folks to
understand when I would ask about the trace with a particular name.
The integration would be a bit more complicated and our tooling and CI
might be impacted but this different design approach. Therefore,
I prefer to be aligned with the old-school.

> 
> Check the usage in lib/test_kprobes.c. Creating the event in sched_tp should be
> the same way when registering for a tracepoint. They both are essentially the
> same.
> 
> Patches to sched_tp module would be welcome ;-)

I cannot promise, but I'll try to find some cycles for it :)

Cheers,
Lukasz

> 
> 
> Cheers
> 
> --
> Qais Yousef
>