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

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Date:   Tue, 8 Sep 2020 13:17:17 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Qais Yousef <qais.yousef@....com>, peterz@...radead.org
Cc:     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 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 tested:

https://lkml.kernel.org/r/20200907091717.26116-1-dietmar.eggemann@arm.com

with our EAS integration which provides one of these tp-2-t2 converter
(sched_tp.c).

http://linux-arm.org/git?p=linux-power.git;a=shortlog;h=refs/heads/topic/tracepoints

[...]