linux-kernel - Re: [PATCH v2] sched/debug: Add new tracepoint to track cpu

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Message-ID: <d3fd557f-e38d-c4b4-1137-fcf0b06d3ba2@arm.com>
Date:   Tue, 8 Sep 2020 18:17:54 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Qais Yousef <qais.yousef@....com>
Cc:     peterz@...radead.org, vincent.donnefort@....com, mingo@...hat.com,
        vincent.guittot@...aro.org, linux-kernel@...r.kernel.org,
        valentin.schneider@....com, Phil Auld <pauld@...hat.com>
Subject: Re: [PATCH v2] sched/debug: Add new tracepoint to track cpu_capacity

On 08/09/2020 17:17, Qais Yousef wrote:
> On 09/08/20 13:17, Dietmar Eggemann wrote:
>> On 07/09/2020 16:51, Qais Yousef wrote:
>>> On 09/07/20 13:13, peterz@...radead.org wrote:
>>>> On Mon, Sep 07, 2020 at 11:48:45AM +0100, Qais Yousef wrote:
>>>>> IMHO the above is a hack. Out-of-tree modules should rely on public headers and
>>>>> exported functions only. What you propose means that people who want to use
>>>>> these tracepoints in meaningful way must have a prebuilt kernel handy. Which is
>>>>> maybe true for us who work in the embedded world. But users who run normal
>>>>> distro kernels (desktop/servers) will fail to build against
>>>>
>>>> But this isn't really aimed at regular users. We're aiming this at
>>>> developers (IIUC) so I dont really see this as a problem.
>>
>> This is what I thought as well. All these helpers can be coded directly
>> in these tracepoint-2-traceevent (tp-2-te) converters. As long as they
>> are build from within kernel/sched/ there is no issue with the export
>> via kernel/sched/sched.h. Otherwise this little trick would be necessary.
>> But since it is a tool for developers I guess we can assume that they
>> can build it from within kernel/sched/.
> 
> I think this will reduce the usefulness of these tracepoints. But if you really
> want to remove them, I am certainly not strongly attached to them and they were
> meant to be removable anyway. So fine by me :-)

I would like to see them go. Less stuff to maintain. And as we see with
the new cpu_capacity tp there are always more helper functions coming.

IMHO, the ability to build those modules via public headers is less
important since they are meant for developers.