linux-kernel - Re: [RESEND][PATCH v2 1/3] sched/tp: Add new tracepoint to track uclamp set from user-space

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Message-ID: <42118979-5f86-75df-72a5-e5fc8592eb82@arm.com>
Date:   Wed, 19 Jul 2023 14:18:17 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        rafael@...nel.org, linux-pm@...r.kernel.org, rostedt@...dmis.org,
        mhiramat@...nel.org, mingo@...hat.com, 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,
        Qais Yousef <qyousef@...alina.io>
Subject: Re: [RESEND][PATCH v2 1/3] sched/tp: Add new tracepoint to track
 uclamp set from user-space



On 7/6/23 12:14, Peter Zijlstra wrote:
> On Wed, May 31, 2023 at 07:26:29PM +0100, Qais Yousef wrote:
>> On 05/22/23 15:57, Lukasz Luba wrote:
>>> The user-space can set uclamp value for a given task. It impacts task
>>> placement decisions made by the scheduler. This is very useful information
>>> and helps to understand the system behavior or track improvements in
>>> middleware and applications which start using uclamp mechanisms and report
>>> better performance in tests.
>>
>> Do you mind adding a generic one instead please? And explain why we can't just
>> attach to the syscall via kprobes? I think you want to bypass the permission
>> checks, so maybe a generic tracepoint after that might be justifiable?
>> Then anyone can use it to track how userspace has changed any attributes for
>> a task, not just uclamp.
> 
> Yeah, so I'm leaning towards the same, if you want to put a tracepoint
> in __sched_setscheduler(), just trace the whole attr and leave it at
> that:
> 
> 	trace_update_sched_attr_tp(p, attr);
> 
> or somesuch.
> 

OK, fair enough, I'll do that. Thanks Peter!
(I'm sorry for the delay, I was on vacation)

Lukasz