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Message-ID: <CAK7LNAQ0RwJYkCXHj8QMH3sqXgY2LBTiYV8HnKD8oANB8Bb+Yg@mail.gmail.com>
Date: Mon, 21 Oct 2024 12:18:16 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Rong Xu <xur@...gle.com>
Cc: Alice Ryhl <aliceryhl@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>,
Arnd Bergmann <arnd@...db.de>, Bill Wendling <morbo@...gle.com>, Borislav Petkov <bp@...en8.de>,
Breno Leitao <leitao@...ian.org>, Brian Gerst <brgerst@...il.com>,
Dave Hansen <dave.hansen@...ux.intel.com>, David Li <davidxl@...gle.com>,
Han Shen <shenhan@...gle.com>, Heiko Carstens <hca@...ux.ibm.com>, "H. Peter Anvin" <hpa@...or.com>,
Ingo Molnar <mingo@...hat.com>, Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
Josh Poimboeuf <jpoimboe@...nel.org>, Juergen Gross <jgross@...e.com>,
Justin Stitt <justinstitt@...gle.com>, Kees Cook <kees@...nel.org>,
"Mike Rapoport (IBM)" <rppt@...nel.org>, Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>, Nicolas Schier <nicolas@...sle.eu>,
"Paul E. McKenney" <paulmck@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
Sami Tolvanen <samitolvanen@...gle.com>, Thomas Gleixner <tglx@...utronix.de>,
Wei Yang <richard.weiyang@...il.com>, workflows@...r.kernel.org,
Miguel Ojeda <miguel.ojeda.sandonis@...il.com>, Maksim Panchenko <max4bolt@...il.com>, x86@...nel.org,
linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
llvm@...ts.linux.dev, Sriraman Tallam <tmsriram@...gle.com>,
Krzysztof Pszeniczny <kpszeniczny@...gle.com>
Subject: Re: [PATCH v4 5/6] AutoFDO: Enable machine function split
optimization for AutoFDO
On Tue, Oct 15, 2024 at 6:33 AM Rong Xu <xur@...gle.com> wrote:
>
> Enable the machine function split optimization for AutoFDO in Clang.
>
> Machine function split (MFS) is a pass in the Clang compiler that
> splits a function into hot and cold parts. The linker groups all
> cold blocks across functions together. This decreases hot code
> fragmentation and improves iCache and iTLB utilization.
>
> MFS requires a profile so this is enabled only for the AutoFDO builds.
>
> Co-developed-by: Han Shen <shenhan@...gle.com>
> Signed-off-by: Han Shen <shenhan@...gle.com>
> Signed-off-by: Rong Xu <xur@...gle.com>
> Suggested-by: Sriraman Tallam <tmsriram@...gle.com>
> Suggested-by: Krzysztof Pszeniczny <kpszeniczny@...gle.com>
> ---
> include/asm-generic/vmlinux.lds.h | 6 ++++++
> scripts/Makefile.autofdo | 2 ++
> 2 files changed, 8 insertions(+)
>
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index ace617d1af9b..20e46c0917db 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -565,9 +565,14 @@ defined(CONFIG_AUTOFDO_CLANG)
> __unlikely_text_start = .; \
> *(.text.unlikely .text.unlikely.*) \
> __unlikely_text_end = .;
> +#define TEXT_SPLIT \
> + __split_text_start = .; \
> + *(.text.split .text.split.[0-9a-zA-Z_]*) \
> + __split_text_end = .;
> #else
> #define TEXT_HOT *(.text.hot .text.hot.*)
> #define TEXT_UNLIKELY *(.text.unlikely .text.unlikely.*)
> +#define TEXT_SPLIT
> #endif
Why conditional?
Where are __unlikely_text_start and __unlikely_text_end used?
--
Best Regards
Masahiro Yamada
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