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

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Message-ID: <3ed3c9a0-8aed-02ad-b7f0-69200441a994@arm.com>
Date:   Tue, 30 May 2023 12:03:27 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Lukasz Luba <lukasz.luba@....com>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, rafael@...nel.org
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
Subject: Re: [PATCH v2 05/17] trace: energy_model: Add trace event for EM
 runtime modifications

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.

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