linux-kernel - Re: [PATCH 2/2] sched/debug: add sched_update_nr

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Message-ID: <CAADnVQJFXq0n1J+vFMwhNgGNBYXK+EsFaE_Zebp84wMOLN8TNA@mail.gmail.com>
Date:   Wed, 4 Sep 2019 10:53:38 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        Qais Yousef <qais.yousef@....com>,
        Valentin Schneider <valentin.schneider@....com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Jirka Hladký <jhladky@...hat.com>,
        Jiří Vozár <jvozar@...hat.com>,
        X86 ML <x86@...nel.org>
Subject: Re: [PATCH 2/2] sched/debug: add sched_update_nr_running tracepoint

On Wed, Sep 4, 2019 at 10:47 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Sep 04, 2019 at 08:51:21AM -0700, Alexei Starovoitov wrote:
> > Anything in tracing can be deleted.
> > Tracing is about debugging and introspection.
> > When underlying kernel code changes the introspection points change as well.
>
> Right; except when it breaks widely used tools; like say powertop. Been
> there, done that.

powertop was a lesson learned, but it's not a relevant example anymore.
There are more widely used tools today. Like bcc tools.
And bpftrace is quickly gaining momentum and large user base.
bcc tools did break already several times and people fixed them.