From: Andi Kleen <ak@linux.intel.com> To: Arvind Sankar <nivedita@alum.mit.edu> Cc: "Kees Cook" <keescook@chromium.org>, "Thomas Gleixner" <tglx@linutronix.de>, "Will Deacon" <will@kernel.org>, "Nick Desaulniers" <ndesaulniers@google.com>, "Jian Cai" <jiancai@google.com>, "Fāng-ruì Sòng" <maskray@google.com>, "Luis Lozano" <llozano@google.com>, "Manoj Gupta" <manojgupta@google.com>, stable@vger.kernel.org, "Catalin Marinas" <catalin.marinas@arm.com>, "Mark Rutland" <mark.rutland@arm.com>, "Ard Biesheuvel" <ardb@kernel.org>, "Peter Collingbourne" <pcc@google.com>, "James Morse" <james.morse@arm.com>, "Borislav Petkov" <bp@suse.de>, "Ingo Molnar" <mingo@redhat.com>, "Russell King" <linux@armlinux.org.uk>, "Masahiro Yamada" <masahiroy@kernel.org>, "Nathan Chancellor" <natechancellor@gmail.com>, "Arnd Bergmann" <arnd@arndb.de>, x86@kernel.org Subject: Re: [PATCH v5 13/36] vmlinux.lds.h: add PGO and AutoFDO input sections Date: Mon, 3 Aug 2020 21:45:32 -0700 [thread overview] Message-ID: <20200804044532.GC1321588@tassilo.jf.intel.com> (raw) In-Reply-To: <20200803201525.GA1351390@rani.riverdale.lan> > Why is that? Both .text and .text.hot have alignment of 2^4 (default > function alignment on x86) by default, so it doesn't seem like it should > matter for packing density. Avoiding interspersing cold text among You may lose part of a cache line on each unit boundary. Linux has a lot of units, some of them small. All these bytes add up. It's bad for TLB locality too. Sadly with all the fine grained protection changes the 2MB coverage is eroding anyways, but this makes it even worse. > regular/hot text seems like it should be a net win. > > That old commit doesn't reference efficiency -- it says there was some > problem with matching when they were separated out, but there were no > wildcard section names back then. It was about efficiency. -Andi
WARNING: multiple messages have this Message-ID (diff)
From: Andi Kleen <ak@linux.intel.com> To: Arvind Sankar <nivedita@alum.mit.edu> Cc: "Kees Cook" <keescook@chromium.org>, "Thomas Gleixner" <tglx@linutronix.de>, "Will Deacon" <will@kernel.org>, "Nick Desaulniers" <ndesaulniers@google.com>, "Jian Cai" <jiancai@google.com>, "Fāng-ruì Sòng" <maskray@google.com>, "Luis Lozano" <llozano@google.com>, "Manoj Gupta" <manojgupta@google.com>, stable@vger.kernel.org, "Catalin Marinas" <catalin.marinas@arm.com>, "Mark Rutland" <mark.rutland@arm.com>, "Ard Biesheuvel" <ardb@kernel.org>, "Peter Collingbourne" <pcc@google.com>, "James Morse" <james.morse@arm.com>, "Borislav Petkov" <bp@suse.de>, "Ingo Molnar" <mingo@redhat.com>, "Russell King" <linux@armlinux.org.uk>, "Masahiro Yamada" <masahiroy@kernel.org>, "Nathan Chancellor" <natechancellor@gmail.com>, "Arnd Bergmann" <arnd@arndb.de>, x86@kernel.org, clang-built-linux@googlegroups.com, linux-arch@vger.kernel.org, linux-efi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, "Michal Marek" <michal.lkml@markovi.net> Subject: Re: [PATCH v5 13/36] vmlinux.lds.h: add PGO and AutoFDO input sections Date: Mon, 3 Aug 2020 21:45:32 -0700 [thread overview] Message-ID: <20200804044532.GC1321588@tassilo.jf.intel.com> (raw) Message-ID: <20200804044532.110BashNM2ubqWfmj27b9k5-RCQ8MFRa6WMGdfLBFqM@z> (raw) In-Reply-To: <20200803201525.GA1351390@rani.riverdale.lan> > Why is that? Both .text and .text.hot have alignment of 2^4 (default > function alignment on x86) by default, so it doesn't seem like it should > matter for packing density. Avoiding interspersing cold text among You may lose part of a cache line on each unit boundary. Linux has a lot of units, some of them small. All these bytes add up. It's bad for TLB locality too. Sadly with all the fine grained protection changes the 2MB coverage is eroding anyways, but this makes it even worse. > regular/hot text seems like it should be a net win. > > That old commit doesn't reference efficiency -- it says there was some > problem with matching when they were separated out, but there were no > wildcard section names back then. It was about efficiency. -Andi
next prev parent reply other threads:[~2020-08-04 4:45 UTC|newest] Thread overview: 97+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-07-31 23:07 [PATCH v5 00/36] Warn on orphan section placement Kees Cook 2020-07-31 23:07 ` Kees Cook 2020-07-31 23:07 ` [PATCH v5 01/36] x86/boot/compressed: Move .got.plt entries out of the .got section Kees Cook 2020-07-31 23:07 ` [PATCH v5 02/36] x86/boot/compressed: Force hidden visibility for all symbol references Kees Cook 2020-07-31 23:07 ` Kees Cook 2020-07-31 23:07 ` [PATCH v5 03/36] x86/boot/compressed: Get rid of GOT fixup code Kees Cook 2020-07-31 23:07 ` [PATCH v5 04/36] x86/boot: Add .text.* to setup.ld Kees Cook 2020-07-31 23:07 ` Kees Cook 2020-07-31 23:07 ` [PATCH v5 05/36] x86/boot: Remove run-time relocations from .head.text code Kees Cook 2020-07-31 23:07 ` Kees Cook 2020-07-31 23:42 ` Nick Desaulniers 2020-07-31 23:42 ` Nick Desaulniers 2020-07-31 23:07 ` [PATCH v5 06/36] x86/boot: Remove run-time relocations from head_{32,64}.S Kees Cook 2020-07-31 23:07 ` Kees Cook 2020-08-07 18:12 ` Nick Desaulniers 2020-08-07 20:20 ` Arvind Sankar 2020-07-31 23:07 ` [PATCH v5 07/36] x86/boot: Check that there are no run-time relocations Kees Cook 2020-07-31 23:07 ` Kees Cook 2020-07-31 23:07 ` [PATCH v5 08/36] vmlinux.lds.h: Create COMMON_DISCARDS Kees Cook 2020-07-31 23:07 ` [PATCH v5 09/36] vmlinux.lds.h: Add .gnu.version* to COMMON_DISCARDS Kees Cook 2020-07-31 23:07 ` [PATCH v5 10/36] vmlinux.lds.h: Avoid KASAN and KCSAN's unwanted sections Kees Cook 2020-07-31 23:07 ` Kees Cook 2020-07-31 23:07 ` [PATCH v5 11/36] vmlinux.lds.h: Split ELF_DETAILS from STABS_DEBUG Kees Cook 2020-07-31 23:07 ` [PATCH v5 12/36] vmlinux.lds.h: Add .symtab, .strtab, and .shstrtab to ELF_DETAILS Kees Cook 2020-07-31 23:07 ` Kees Cook 2020-07-31 23:07 ` [PATCH v5 13/36] vmlinux.lds.h: add PGO and AutoFDO input sections Kees Cook 2020-07-31 23:07 ` Kees Cook 2020-08-01 3:51 ` Arvind Sankar 2020-08-01 3:51 ` Arvind Sankar 2020-08-01 6:18 ` Kees Cook 2020-08-01 6:18 ` Kees Cook 2020-08-01 17:27 ` Arvind Sankar 2020-08-01 17:27 ` Arvind Sankar 2020-08-03 19:05 ` Andi Kleen 2020-08-03 19:05 ` Andi Kleen 2020-08-03 20:15 ` Arvind Sankar 2020-08-03 20:15 ` Arvind Sankar 2020-08-04 1:19 ` Fāng-ruì Sòng 2020-08-04 1:19 ` Fāng-ruì Sòng 2020-08-04 4:45 ` Andi Kleen [this message] 2020-08-04 4:45 ` Andi Kleen 2020-08-04 5:32 ` Fāng-ruì Sòng 2020-08-04 5:32 ` Fāng-ruì Sòng 2020-08-04 16:06 ` Arvind Sankar 2020-08-04 16:06 ` Arvind Sankar 2020-08-21 19:18 ` Kees Cook 2020-07-31 23:07 ` [PATCH v5 14/36] efi/libstub: Disable -mbranch-protection Kees Cook 2020-07-31 23:07 ` [PATCH v5 15/36] arm64/mm: Remove needless section quotes Kees Cook 2020-07-31 23:07 ` Kees Cook 2020-07-31 23:08 ` [PATCH v5 16/36] arm64/kernel: Remove needless Call Frame Information annotations Kees Cook 2020-07-31 23:08 ` Kees Cook 2020-07-31 23:08 ` [PATCH v5 17/36] arm64/build: Remove .eh_frame* sections due to unwind tables Kees Cook 2020-07-31 23:08 ` [PATCH v5 18/36] arm64/build: Use common DISCARDS in linker script Kees Cook 2020-07-31 23:08 ` [PATCH v5 19/36] arm64/build: Add missing DWARF sections Kees Cook 2020-07-31 23:08 ` [PATCH v5 20/36] arm64/build: Assert for unwanted sections Kees Cook 2020-07-31 23:08 ` [PATCH v5 21/36] arm64/build: Warn on orphan section placement Kees Cook 2020-07-31 23:08 ` Kees Cook 2020-07-31 23:08 ` [PATCH v5 22/36] arm/build: Refactor linker script headers Kees Cook 2020-07-31 23:08 ` Kees Cook 2020-07-31 23:08 ` [PATCH v5 23/36] arm/build: Explicitly keep .ARM.attributes sections Kees Cook 2020-07-31 23:08 ` Kees Cook 2020-08-03 19:02 ` Nick Desaulniers 2020-08-03 19:02 ` Nick Desaulniers 2020-08-17 22:06 ` Fangrui Song 2020-07-31 23:08 ` [PATCH v5 24/36] arm/build: Add missing sections Kees Cook 2020-07-31 23:08 ` Kees Cook 2020-07-31 23:08 ` [PATCH v5 25/36] arm/build: Warn on orphan section placement Kees Cook 2020-07-31 23:08 ` [PATCH v5 26/36] arm/boot: Handle all sections explicitly Kees Cook 2020-07-31 23:08 ` Kees Cook 2020-07-31 23:08 ` [PATCH v5 27/36] arm/boot: Warn on orphan section placement Kees Cook 2020-07-31 23:08 ` [PATCH v5 28/36] x86/asm: Avoid generating unused kprobe sections Kees Cook 2020-07-31 23:08 ` Kees Cook 2020-07-31 23:08 ` [PATCH v5 29/36] x86/build: Enforce an empty .got.plt section Kees Cook 2020-08-01 2:12 ` Arvind Sankar 2020-08-01 5:32 ` Kees Cook 2020-08-21 17:49 ` Kees Cook 2020-07-31 23:08 ` [PATCH v5 30/36] x86/build: Assert for unwanted sections Kees Cook 2020-07-31 23:08 ` Kees Cook 2020-07-31 23:08 ` [PATCH v5 31/36] x86/build: Warn on orphan section placement Kees Cook 2020-07-31 23:08 ` [PATCH v5 32/36] x86/boot/compressed: Reorganize zero-size section asserts Kees Cook 2020-07-31 23:08 ` Kees Cook 2020-08-01 1:47 ` Arvind Sankar 2020-08-01 2:53 ` Arvind Sankar 2020-08-01 2:53 ` Arvind Sankar 2020-08-01 5:36 ` Kees Cook 2020-08-01 17:12 ` Arvind Sankar 2020-08-21 18:24 ` Kees Cook 2020-08-01 5:35 ` Kees Cook 2020-08-01 5:35 ` Kees Cook 2020-08-01 17:00 ` Arvind Sankar 2020-08-21 18:19 ` Kees Cook 2020-07-31 23:08 ` [PATCH v5 33/36] x86/boot/compressed: Remove, discard, or assert for unwanted sections Kees Cook 2020-07-31 23:08 ` Kees Cook 2020-07-31 23:08 ` [PATCH v5 34/36] x86/boot/compressed: Add missing debugging sections to output Kees Cook 2020-07-31 23:08 ` Kees Cook 2020-07-31 23:08 ` [PATCH v5 35/36] x86/boot/compressed: Warn on orphan section placement Kees Cook 2020-07-31 23:08 ` [PATCH v5 36/36] arm/build: Assert for unwanted sections Kees Cook
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