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

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Date:   Thu, 6 Jul 2023 13:14:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Qais Yousef <qyousef@...alina.io>
Cc:     Lukasz Luba <lukasz.luba@....com>, 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
Subject: Re: [RESEND][PATCH v2 1/3] sched/tp: Add new tracepoint to track
 uclamp set from user-space

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.