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Date:   Mon, 14 Jun 2021 09:51:31 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Bill Wendling <morbo@google.com>
Cc:     Kees Cook <keescook@google.com>, Jonathan Corbet <corbet@lwn.net>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Sami Tolvanen <samitolvanen@google.com>,
        Fangrui Song <maskray@google.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>
Subject: Re: [PATCH v9] pgo: add clang's Profile Guided Optimization
 infrastructure
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On Sat, Jun 12, 2021 at 01:56:41PM -0700, Bill Wendling wrote:
> For example, Fangrui gave you numbers, and you rejected them out of
> hand. I've explained to you why instrumentation is better than
> sampling (at least for clang). Fangrui gave you numbers. Let's move on
> to something else.

I did not dismiss them; I asked for clarification. I would like to
understand what exactly is missed by sampling based PGO data that makes
such a difference.