linux-kernel - Re: [GIT PULL] Clang feature updates for v5.14-rc1

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Date:   Tue, 29 Jun 2021 14:57:49 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bill Wendling <morbo@...gle.com>,
        Bill Wendling <wcw@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Fangrui Song <maskray@...gle.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Jarmo Tiitto <jarmo.tiitto@...il.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [GIT PULL] Clang feature updates for v5.14-rc1

On Tue, Jun 29, 2021 at 2:27 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> Right now we're having trouble with hardware performance counters on
> non-intel chips; I don't think we have working LBR equivalents on AMD
> until zen3, and our ETM based samples on ARM are hung up on a few last
> minute issues requiring new hardware (from multiple different chipset
> vendors).

I agree that perf profiling works best on Intel. The AMD perf side
works ok in Zen 2 from what I've seen, but needs to be a full-system
profile ("perf record -a") to use the better options, and ARM is..

But with x86 ranging from "excellent" to "usable", and ARM hopefully
being at least close to getting better proper profile data, I really
think it's the way forward, with instrumentation being a band-aid at
best.

             Linus