From: Jarmo Tiitto <jarmo.tiitto@gmail.com>
To: Kees Cook <keescook@chromium.org>
Cc: Daniel Axtens <dja@axtens.net>,
Mark Rutland <mark.rutland@arm.com>,
catalin.marinas@arm.com, clang-built-linux@googlegroups.com,
hca@linux.ibm.com, jarmo.tiitto@gmail.com,
linux-kernel@vger.kernel.org, lukas.bulwahn@gmail.com,
masahiroy@kernel.org, maskray@google.com, morbo@google.com,
nathan@kernel.org, ndesaulniers@google.com,
oberpar@linux.ibm.com, ojeda@kernel.org, peterz@infradead.org,
samitolvanen@google.com, torvalds@linux-foundation.org,
wcw@google.com, will@kernel.org
Subject: Re: ARCH_WANTS_NO_INSTR (Re: [GIT PULL] Clang feature updates for v5.14-rc1)
Date: Thu, 07 Oct 2021 09:19:29 +0300 [thread overview]
Message-ID: <1803114.lsCNsgVnni@hyperiorarchmachine> (raw)
In-Reply-To: <20211005143003.GC6678@C02TD0UTHF1T.local>
Mark Rutland wrote tiistaina 5. lokakuuta 2021 17.30.03 EEST:
> On Wed, Oct 06, 2021 at 12:10:15AM +1100, Daniel Axtens wrote:
> > Hi,
>
> Hi Daniel,
>
> > Apologies, I can't find the original email for this:
> > > Kconfig: Introduce ARCH_WANTS_NO_INSTR and CC_HAS_NO_PROFILE_FN_ATTR
> >
> > which is now commit 51c2ee6d121c ("Kconfig: Introduce ARCH_WANTS_NO_INSTR
> > and
> > CC_HAS_NO_PROFILE_FN_ATTR"). It doesn't seem to show up on Google, this
was
> > the best I could find.
>
> Unless I've misunderstood, the commit title was rewritten when the patch
> was applied, from the third link in commit 51c2ee6d121c. For reference,
> those three links are:
>
> Link:
> https://lore.kernel.org/lkml/YMTn9yjuemKFLbws@hirez.programming.kicks-ass.net
> / Link:
> https://lore.kernel.org/lkml/YMcssV%2Fn5IBGv4f0@hirez.programming.kicks-ass.n
> et/ Link:
> https://lore.kernel.org/r/20210621231822.2848305-4-ndesaulniers@google.com
Hello, Kees and others cc'd !
I got above mail, and went through an rabbit hole of lkml messages since I was
involved with the clang-pgo feature.
I'll like to know what is the current situation about GCOV and PGO?
I saw that for-next/clang/pgo had some new interesting patches applied.
Would it be good time now to continue make instrumented kernel?
Background:
I essentially stopped my work at the point where Peter Z noted -fprofile-
generate breaks the kernel+gcov and noinstr needs to be fixed.
My situation here is that I have very old non-public PGO hacks that date back
to v4.11 - v4.19 era using GCOV subsystem and now with the newer clang-pgo
patches that are in usable state.
These previous attempts all broke apart because of the noinstr not doing it's
job with -fprofile-generate: the compiler could generate a call to gcov/pgo
profiler hook in wrong place (in interrupt context, If I remember) and the
kernel was doomed.
One thing has not changed over the years: I still don't have a single CPU that
has hardware PMU capable of LBR and generating AutoFDO profiles. :(
So I have written code/hacks now for two subsystems to gain profile data for
PGO. In the end, I don't care from what instrumented kernel pipes I have to
pull the data out, and what format it is in, as long as the compiler accepts
it. :-P
PS: gcov-pgo had waayy too many pipes for doing just pgo. /s
Well, that was my past on this PGO topic.
Thanks all,
-Jarmo Tiitto
prev parent reply other threads:[~2021-10-07 6:19 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
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 [this message]
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