Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 2 Jul 2021 20:57:39 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Bill Wendling <morbo@google.com>,
        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>,
        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
Message-ID: <YN9ho7yDFStVw8g3@hirez.programming.kicks-ass.net>
References: <202106281231.E99B92BB13@keescook>
 <CAHk-=whqCT0BeqBQhW8D-YoLLgp_eFY=8Y=9ieREM5xx0ef08w@mail.gmail.com>
 <202106291311.20AB10D04@keescook>
 <CAHk-=wg8M2DyA=bWtnGsAOVqYU-AusxYcpXubUO2htb6qPU9dg@mail.gmail.com>
 <CAGG=3QXrOnN3-3r-VGDpmikKRpaK_p5hM_qHGprDDMuFNKuifA@mail.gmail.com>
 <YN8NGLPQ4Cqanc48@hirez.programming.kicks-ass.net>
 <CAKwvOd=-qdp6xcuVb-fSni6X-0UuJ6GM5+TJdWSkAfvNmqfZ+w@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAKwvOd=-qdp6xcuVb-fSni6X-0UuJ6GM5+TJdWSkAfvNmqfZ+w@mail.gmail.com>
Precedence: bulk

On Fri, Jul 02, 2021 at 10:26:40AM -0700, Nick Desaulniers wrote:
> On Fri, Jul 2, 2021 at 5:57 AM Peter Zijlstra <peterz@infradead.org> wrote:

> > I've asked this before; *what* is missing from LBR samples that's
> > reponsible for the performance gap?
> 
> Are we able to collect LBR samples from __init code?  I can imagine
> trying to launch perf from init/pid 1, but I suspect at that point
> it's way too late.
> 
> Increasingly, boot times of hosts (and virtualized guests) are
> becoming important to us, both in the datacenters and on mobile.

For a guest, possibly, I've no idea how any of that virt crud works.