linux-kernel - Re: [RESEND][PATCH v2 3/3] schedutil: trace: Add tracing to capture filter out requests

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Message-ID: <a464e8ee-a1b9-10dd-5be0-d9dee994d7b8@arm.com>
Date:   Tue, 20 Jun 2023 19:08:12 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-pm@...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,
        qyousef@...alina.io, kernel test robot <lkp@...el.com>
Subject: Re: [RESEND][PATCH v2 3/3] schedutil: trace: Add tracing to capture
 filter out requests

Hi Rafael,

On 6/20/23 18:40, Rafael J. Wysocki wrote:
> On Mon, May 22, 2023 at 4:57 PM Lukasz Luba <lukasz.luba@....com> 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.
>>
>> Reported-by: kernel test robot <lkp@...el.com> # solved tricky build
>> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
>> ---
>>   include/trace/events/sched.h     |  4 ++++
>>   kernel/sched/cpufreq_schedutil.c | 10 ++++++++--
>>   2 files changed, 12 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
>> index dbfb30809f15..e34b7cd5de73 100644
>> --- a/include/trace/events/sched.h
>> +++ b/include/trace/events/sched.h
>> @@ -739,6 +739,10 @@ DECLARE_TRACE(uclamp_update_tsk_tp,
>>          TP_PROTO(struct task_struct *tsk, int uclamp_id,  unsigned int value),
>>          TP_ARGS(tsk, uclamp_id, value));
>>
>> +DECLARE_TRACE(schedutil_update_filtered_tp,
>> +       TP_PROTO(int cpu),
>> +       TP_ARGS(cpu));
>> +
>>   #endif /* _TRACE_SCHED_H */
>>
>>   /* This part must be outside protection */
>> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
>> index f462496e5c07..4f9daf258a65 100644
>> --- a/kernel/sched/cpufreq_schedutil.c
>> +++ b/kernel/sched/cpufreq_schedutil.c
>> @@ -6,6 +6,8 @@
>>    * Author: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>    */
>>
>> +EXPORT_TRACEPOINT_SYMBOL_GPL(schedutil_update_filtered_tp);
>> +
>>   #define IOWAIT_BOOST_MIN       (SCHED_CAPACITY_SCALE / 8)
>>
>>   struct sugov_tunables {
>> @@ -318,8 +320,10 @@ static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu,
>>
>>          ignore_dl_rate_limit(sg_cpu);
>>
>> -       if (!sugov_should_update_freq(sg_cpu->sg_policy, time))
>> +       if (!sugov_should_update_freq(sg_cpu->sg_policy, time)) {
>> +               trace_schedutil_update_filtered_tp(sg_cpu->cpu);
> 
> It looks like the tracepoint can be added to
> sugov_should_update_freq() for less code duplication.
> 

Make sense. I will move that trace there.

In such case, of movement that trace call...
Based on your comment for patch 2/3 I got impression
that you still want it. For me it looks more 'aligned' w/ that
patch 2/3. The two functions code flows:
sugov_update_shared() and sugov_update_single_common() - how
they call and interpret result from
sugov_should_update_freq() - is more clear IMO.

So I will keep that patch 2/3 in the next version. Although,
if you don't like it - please tell me and I will drop it.

Thanks for the review!

Lukasz