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

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Message-ID: <CAADnVQ+Cwe27pwTwJ3TNiatKe8dXAwXBf_2jJDqxB0RFUbr7_A@mail.gmail.com>
Date:   Wed, 4 Sep 2019 08:37:22 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        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>, Qais Yousef <qais.yousef@....com>
Subject: Re: [PATCH 2/2] sched/debug: add sched_update_nr_running tracepoint

On Wed, Sep 4, 2019 at 8:33 AM Joel Fernandes <joel@...lfernandes.org> wrote:
>
> On Wed, Sep 04, 2019 at 08:26:52AM -0700, Alexei Starovoitov wrote:
> > On Wed, Sep 4, 2019 at 6:14 AM Joel Fernandes <joel@...lfernandes.org> wrote:
> > >
> > > True. However, for kprobes-based BPF program - it does check for kernel
> > > version to ensure that the BPF program is built against the right kernel
> > > version (in order to ensure the program is built against the right set of
> > > kernel headers). If it is not, then BPF refuses to load the program.
> >
> > This is not true anymore. Users found few ways to workaround that check
> > in practice. It became useless and it was deleted some time ago.
>
> Wow, Ok! Interesting!

the other part of your email says about kernel header requirement.
This is not true any more as well :)
BTF relocations are already supported by the kernel, llvm, libbpf,
bpftool, pahole.
We'll be posting sample code soon.