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

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Message-ID: <20200907111320.GP2674@hirez.programming.kicks-ass.net>
Date:   Mon, 7 Sep 2020 13:13:20 +0200
From:   peterz@...radead.org
To:     Qais Yousef <qais.yousef@....com>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        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 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.

> FWIW, I did raise this concern with Peter in 2019 OSPM and he was okay with the
> exports as it's still not a contract and they can disappear anytime we want.
> Migrating to using BTF is the right way forward IMO. I don't think what we have
> here is out-of-control yet. Though I agree they're annoying.

Right, we're hiding behind the explicit lack of ABI for modules.

Anyway, CTF/BTF/random other crap that isn't DWARFs should work fine to
replace all this muck. Just no idea what the state of any of that is.