Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <3ed3c9a0-8aed-02ad-b7f0-69200441a994@arm.com>
Date:   Tue, 30 May 2023 12:03:27 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.10.0
Subject: Re: [PATCH v2 05/17] trace: energy_model: Add trace event for EM
 runtime modifications
Content-Language: en-US
To:     Lukasz Luba <lukasz.luba@arm.com>, linux-kernel@vger.kernel.org,
        linux-pm@vger.kernel.org, rafael@kernel.org
Cc:     rui.zhang@intel.com, amit.kucheria@verdurent.com,
        amit.kachhap@gmail.com, daniel.lezcano@linaro.org,
        viresh.kumar@linaro.org, len.brown@intel.com, pavel@ucw.cz,
        Pierre.Gondois@arm.com, ionela.voinescu@arm.com,
        rostedt@goodmis.org, mhiramat@kernel.org
References: <20230512095743.3393563-1-lukasz.luba@arm.com>
 <20230512095743.3393563-6-lukasz.luba@arm.com>
From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
In-Reply-To: <20230512095743.3393563-6-lukasz.luba@arm.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

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.

[...]