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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 17 Dec 2020 13:15:46 -0800
Message-ID: <CAHk-=wiTnbrD0zfOaSkwQX0+OB0LE0EjD=+Zxsy2A36-ye+_6Q@mail.gmail.com>
Subject: Re: [PATCH] dcookies: Make dcookies depend on CONFIG_OPROFILE
To:     Arnd Bergmann <arnd@kernel.org>
Cc:     William Cohen <wcohen@redhat.com>,
        Christoph Hellwig <hch@infradead.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Anmar Oueja <anmar.oueja@linaro.org>,
        Arnd Bergmann <arnd@arndb.de>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Just reviving this thread to see if we could get rid of the OPROFILE
kernel code this time..

One option is to just start off with adding a

        depends on DISABLED

on the OPROFILE config option, and see if anybody even notices.

But honestly, just removing the entirely might be the better thing.

The oprofile config is a bit odd. We have things like
OPROFILE_NMI_TIMER which defaults to on even if OPROFILE isn't even
selected. All the _users_ of that seem to be inside oprofile code, so
it's effectively a no-op without oprofile,

The only reason I noticed was that I looked at the Fedora kernel
config files, and went "uhhuh, Fedora still enables that", and had a
quick worry before I noticed that it's just the Kconfig system being
silly.

              Linus

On Wed, Oct 28, 2020 at 11:01 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> On Wed, Oct 28, 2020 at 5:34 PM William Cohen <wcohen@redhat.com> wrote:
> >
> > On 10/27/20 12:54 PM, Linus Torvalds wrote:
> > >
> > > I think the user-space "oprofile" program doesn't actually use the
> > > legacy kernel code any more, and hasn't for a long time.
> >
> > Yes, current OProfile code uses the existing linux perf infrastructure and
> > doesn't use the old oprofile kernel code.  I have thought about removing
> > that old oprofile driver code from kernel, but have not submitted patches
> > for it. I would be fine with eliminating that code from the kernel.
>
> I notice that arch/ia64/ supports oprofile but not perf. I suppose this just
> means that ia64 people no longer care enough about profiling to
> add perf support, but it wouldn't stop us from dropping it, right?
>
> There is also a stub implementation of oprofile for microblaze
> and no perf code, not sure if it would make any difference for them.
>
> Everything else that has oprofile kernel code also supports perf.
>
>        Arnd