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Message-ID: <CAK7LNAQpFdHxAGk1SSRrJwyKA1XjfJLbyAeka7-YemJ1zEevnQ@mail.gmail.com> Date: Mon, 21 Oct 2024 11:25:24 +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> Subject: Re: [PATCH v4 4/6] AutoFDO: Enable -ffunction-sections for the AutoFDO build On Tue, Oct 15, 2024 at 6:33 AM Rong Xu <xur@...gle.com> wrote: > > Enable -ffunction-sections by default for the AutoFDO build. > > With -ffunction-sections, the compiler places each function in its own > section named .text.function_name instead of placing all functions in > the .text section. In the AutoFDO build, this allows the linker to > utilize profile information to reorganize functions for improved > utilization of iCache and iTLB. > > 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> > --- > include/asm-generic/vmlinux.lds.h | 37 ++++++++++++++++++++++++------- > scripts/Makefile.autofdo | 2 +- > 2 files changed, 30 insertions(+), 9 deletions(-) > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > index 5df589c60401..ace617d1af9b 100644 > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -95,18 +95,25 @@ > * With LTO_CLANG, the linker also splits sections by default, so we need > * these macros to combine the sections during the final link. > * > + * With LTO_CLANG, the linker also splits sections by default, so we need > + * these macros to combine the sections during the final link. > + * > * RODATA_MAIN is not used because existing code already defines .rodata.x > * sections to be brought in with rodata. > */ > -#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) > +#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) || \ > +defined(CONFIG_AUTOFDO_CLANG) > #define TEXT_MAIN .text .text.[0-9a-zA-Z_]* > +#else > +#define TEXT_MAIN .text > +#endif > +#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) > #define DATA_MAIN .data .data.[0-9a-zA-Z_]* .data..L* .data..compoundliteral* .data.$__unnamed_* .data.$L* > #define SDATA_MAIN .sdata .sdata.[0-9a-zA-Z_]* > #define RODATA_MAIN .rodata .rodata.[0-9a-zA-Z_]* .rodata..L* > #define BSS_MAIN .bss .bss.[0-9a-zA-Z_]* .bss..L* .bss..compoundliteral* > #define SBSS_MAIN .sbss .sbss.[0-9a-zA-Z_]* > #else > -#define TEXT_MAIN .text > #define DATA_MAIN .data > #define SDATA_MAIN .sdata > #define RODATA_MAIN .rodata > @@ -549,6 +556,20 @@ > __cpuidle_text_end = .; \ > __noinstr_text_end = .; > > +#ifdef CONFIG_AUTOFDO_CLANG > +#define TEXT_HOT \ > + __hot_text_start = .; \ > + *(.text.hot .text.hot.*) \ > + __hot_text_end = .; > +#define TEXT_UNLIKELY \ > + __unlikely_text_start = .; \ > + *(.text.unlikely .text.unlikely.*) \ > + __unlikely_text_end = .; > +#else > +#define TEXT_HOT *(.text.hot .text.hot.*) > +#define TEXT_UNLIKELY *(.text.unlikely .text.unlikely.*) > +#endif Again, why is this conditional? The only difference is *_start and *_end symbols are defined when CONFIG_AUTOFDO_CLANG=y. And, where are these symbols used? > + > /* > * .text section. Map to function alignment to avoid address changes > * during second ld run in second ld pass when generating System.map > @@ -557,30 +578,30 @@ > * code elimination or function-section is enabled. Match these symbols > * first when in these builds. > */ > -#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) > +#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) || \ > +defined(CONFIG_AUTOFDO_CLANG) > #define TEXT_TEXT \ > ALIGN_FUNCTION(); \ > *(.text.asan.* .text.tsan.*) \ > *(.text.unknown .text.unknown.*) \ > - *(.text.unlikely .text.unlikely.*) \ > + TEXT_UNLIKELY \ > . = ALIGN(PAGE_SIZE); \ > - *(.text.hot .text.hot.*) \ > + TEXT_HOT \ > *(TEXT_MAIN .text.fixup) \ > NOINSTR_TEXT \ > *(.ref.text) > #else > #define TEXT_TEXT \ > ALIGN_FUNCTION(); \ > - *(.text.hot .text.hot.*) \ > + TEXT_HOT \ > *(TEXT_MAIN .text.fixup) \ > - *(.text.unlikely .text.unlikely.*) \ > + TEXT_UNLIKELY \ > *(.text.unknown .text.unknown.*) \ > NOINSTR_TEXT \ > *(.ref.text) \ > *(.text.asan.* .text.tsan.*) > #endif > > - > /* sched.text is aling to function alignment to secure we have same > * address even at second ld pass when generating System.map */ > #define SCHED_TEXT \ > diff --git a/scripts/Makefile.autofdo b/scripts/Makefile.autofdo > index 1c9f224bc221..9c9a530ef090 100644 > --- a/scripts/Makefile.autofdo > +++ b/scripts/Makefile.autofdo > @@ -10,7 +10,7 @@ ifndef CONFIG_DEBUG_INFO > endif > > ifdef CLANG_AUTOFDO_PROFILE > - CFLAGS_AUTOFDO_CLANG += -fprofile-sample-use=$(CLANG_AUTOFDO_PROFILE) > + CFLAGS_AUTOFDO_CLANG += -fprofile-sample-use=$(CLANG_AUTOFDO_PROFILE) -ffunction-sections > endif > > ifdef CONFIG_LTO_CLANG_THIN > -- > 2.47.0.rc1.288.g06298d1525-goog > > -- Best Regards Masahiro Yamada
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