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Date:   Thu, 6 Jul 2023 13:14:43 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Qais Yousef <qyousef@layalina.io>
Cc:     Lukasz Luba <lukasz.luba@arm.com>, linux-kernel@vger.kernel.org,
        linux-trace-kernel@vger.kernel.org, rafael@kernel.org,
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        mingo@redhat.com, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        bsegall@google.com, mgorman@suse.de, bristot@redhat.com,
        vschneid@redhat.com, delyank@fb.com, qyousef@google.com
Subject: Re: [RESEND][PATCH v2 1/3] sched/tp: Add new tracepoint to track
 uclamp set from user-space
Message-ID: <20230706111443.GH2833176@hirez.programming.kicks-ass.net>
References: <20230522145702.2419654-1-lukasz.luba@arm.com>
 <20230522145702.2419654-2-lukasz.luba@arm.com>
 <20230531182629.nztie5rwhjl53v3d@airbuntu>
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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.