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

[Lukasz Luba]

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