From: Peter Zijlstra <peterz@infradead.org>
To: Bill Wendling <morbo@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Kees Cook <keescook@chromium.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Bill Wendling <wcw@google.com>,
Catalin Marinas <catalin.marinas@arm.com>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Fangrui Song <maskray@google.com>,
Heiko Carstens <hca@linux.ibm.com>,
Jarmo Tiitto <jarmo.tiitto@gmail.com>,
Lukas Bulwahn <lukas.bulwahn@gmail.com>,
Mark Rutland <mark.rutland@arm.com>,
Masahiro Yamada <masahiroy@kernel.org>,
Miguel Ojeda <ojeda@kernel.org>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Peter Oberparleiter <oberpar@linux.ibm.com>,
Sami Tolvanen <samitolvanen@google.com>,
Will Deacon <will@kernel.org>
Subject: Re: [GIT PULL] Clang feature updates for v5.14-rc1
Date: Fri, 2 Jul 2021 14:56:56 +0200 [thread overview]
Message-ID: <YN8NGLPQ4Cqanc48@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAGG=3QXrOnN3-3r-VGDpmikKRpaK_p5hM_qHGprDDMuFNKuifA@mail.gmail.com>
On Fri, Jul 02, 2021 at 05:46:46AM -0700, Bill Wendling wrote:
> On Tue, Jun 29, 2021 at 2:04 PM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > On Tue, Jun 29, 2021 at 1:44 PM Kees Cook <keescook@chromium.org> wrote:
> > > >
> > > > And it causes the kernel to be bigger and run slower.
> > >
> > > Right -- that's expected. It's not designed to be the final kernel
> > > someone uses. :)
> >
> > Well, from what I've seen, you actually want to run real loads in
> > production environments for PGO to actually be anything but a bogus
> > "performance benchmarks only" kind of thing.
> >
> The reason we use PGO in this way is because we _cannot_ release a
> kernel into production that hasn't had PGO applied to it. The
> performance of a non-PGO'ed kernel is a non-starter for rollout. We
> try our best to replicate this environment for the benchmarks, which
> is the only sane way to do this. I can't imagine that we're the only
> ones who run up against this chicken-and-egg problem.
>
> For why we don't use sampling, PGO gives a better performance boost
> from an instrumented kernel rather than a sampled profile. I'll work
> on getting statistics to show this.
I've asked this before; *what* is missing from LBR samples that's
reponsible for the performance gap?
next prev parent reply other threads:[~2021-07-02 12:57 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-28 19:32 [GIT PULL] Clang feature updates for v5.14-rc1 Kees Cook
2021-06-29 2:49 ` Linus Torvalds
2021-06-29 20:44 ` Kees Cook
2021-06-29 21:03 ` Linus Torvalds
2021-06-29 21:27 ` Nick Desaulniers
2021-06-29 21:57 ` Linus Torvalds
2021-07-07 8:10 ` Ingo Molnar
2021-07-02 12:46 ` Bill Wendling
2021-07-02 12:56 ` Peter Zijlstra [this message]
2021-07-02 17:26 ` Nick Desaulniers
2021-07-02 18:57 ` Peter Zijlstra
2021-07-02 19:53 ` Nick Desaulniers
2022-10-31 23:55 ` Bill Wendling
2021-06-29 13:14 ` Mark Rutland
2021-06-29 20:11 ` Kees Cook
2021-06-29 21:05 ` Nick Desaulniers
2021-10-05 13:10 ` ARCH_WANTS_NO_INSTR (Re: [GIT PULL] Clang feature updates for v5.14-rc1) Daniel Axtens
2021-10-05 13:45 ` Daniel Axtens
2021-10-05 14:30 ` Mark Rutland
2021-10-07 6:19 ` Jarmo Tiitto
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