linux-kernel - Re: [PATCH v2 05/17] trace: energy_model: Add trace event for EM runtime modifications

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Message-ID: <d871465b-4774-5b62-79a3-9e5325cf8b18@arm.com>
Date:   Mon, 3 Jul 2023 16:53:42 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     rui.zhang@...el.com, amit.kucheria@...durent.com,
        amit.kachhap@...il.com, daniel.lezcano@...aro.org,
        viresh.kumar@...aro.org, len.brown@...el.com, pavel@....cz,
        Pierre.Gondois@....com, ionela.voinescu@....com,
        rostedt@...dmis.org, mhiramat@...nel.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        rafael@...nel.org
Subject: Re: [PATCH v2 05/17] trace: energy_model: Add trace event for EM
 runtime modifications



On 5/30/23 11:03, Dietmar Eggemann wrote:
> On 12/05/2023 11:57, Lukasz Luba wrote:
>> The Energy Model (EM) supports runtime modifications. Track the changes
>> in order to do post-processing analysis. Don't use arrays in the trace
>> event, since they are not properly supported by the tools. Instead use
>> simple "unroll" with emitting the trace event for each EM array entry
>> with proper ID information. The older debugging mechanism which was
>> the simple debugfs which dumping the EM content won't be sufficient for
>> the modifiable EM purpose. This trace event mechanism would address the
>> needs.
> 
> Do we really need a full trace_event for this? Can we not follow the
> task scheduler rule which says no new trace_events and use a trace_point
> here? The footprint in the kernel would be so much smaller.
> 
> E.g. pelt_cfs_tp
> 
> 0 sched.h  694 DECLARE_TRACE(pelt_cfs_tp,
> 1 core.c   106 EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_cfs_tp);
> 2 fair.c  3937 trace_pelt_cfs_tp(cfs_rq);
> 
> And then this patch should be after the section with the functional changes.
> 
> [...]

I agree. I will change that approach and create tracepoint. Also, I'll
move it to the patch at the end of the functional changes.