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Message-ID: <42118979-5f86-75df-72a5-e5fc8592eb82@arm.com>
Date:   Wed, 19 Jul 2023 14:18:17 +0100
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Subject: Re: [RESEND][PATCH v2 1/3] sched/tp: Add new tracepoint to track
 uclamp set from user-space
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To:     Peter Zijlstra <peterz@infradead.org>
Cc:     linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
        rafael@kernel.org, linux-pm@vger.kernel.org, rostedt@goodmis.org,
        mhiramat@kernel.org, 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,
        Qais Yousef <qyousef@layalina.io>
References: <20230522145702.2419654-1-lukasz.luba@arm.com>
 <20230522145702.2419654-2-lukasz.luba@arm.com>
 <20230531182629.nztie5rwhjl53v3d@airbuntu>
 <20230706111443.GH2833176@hirez.programming.kicks-ass.net>
From:   Lukasz Luba <lukasz.luba@arm.com>
In-Reply-To: <20230706111443.GH2833176@hirez.programming.kicks-ass.net>
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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