| Message ID | 20220628210407.3343118-1-ndesaulniers@google.com |
|---|---|
| State | New |
| Headers | show |
| Series | kbuild: drop support for CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 | expand |
On Tuesday, 28 June 2022 23:04:07 CEST Nick Desaulniers wrote: > The difference in most compilers between `-O3` and `-O2` is mostly down > to whether loops with statically determinable trip counts are fully > unrolled vs unrolled to a multiple of SIMD width. > > This patch is effectively a revert of > commit 15f5db60a137 ("kbuild,arc: add > CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 for ARC") without re-adding > ARCH_CFLAGS > > Ever since > commit cfdbc2e16e65 ("ARC: Build system: Makefiles, Kconfig, Linker > script") > ARC has been built with -O3, though the reason for doing so was not > specified in inline comments or the commit message. This commit does not > re-add -O3 to arch/arc/Makefile. > > Folks looking to experiment with `-O3` (or any compiler flag for that > matter) may pass them along to the command line invocation of make: > > $ make KCFLAGS=-O3 > > Code that looks to re-add an explicit Kconfig option for `-O3` should > provide: > 1. A rigorous and reproducible performance profile of a reasonable > userspace workload that demonstrates a hot loop in the kernel that > would benefit from `-O3` over `-O2`. > 2. Disassembly of said loop body before and after. > 3. Provides stats on terms of increase in file size. > Might be worth cleaning up the rest of the kernel of instances of -O3, too. -O3 used to build lz4 and mips vdso, for instance. Might be a bit of a digression, though -- ~miko
On Wed, Jun 29, 2022 at 6:06 AM Nick Desaulniers <ndesaulniers@google.com> wrote: > > The difference in most compilers between `-O3` and `-O2` is mostly down > to whether loops with statically determinable trip counts are fully > unrolled vs unrolled to a multiple of SIMD width. > > This patch is effectively a revert of > commit 15f5db60a137 ("kbuild,arc: add > CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 for ARC") without re-adding > ARCH_CFLAGS > > Ever since > commit cfdbc2e16e65 ("ARC: Build system: Makefiles, Kconfig, Linker > script") > ARC has been built with -O3, though the reason for doing so was not > specified in inline comments or the commit message. This commit does not > re-add -O3 to arch/arc/Makefile. > > Folks looking to experiment with `-O3` (or any compiler flag for that > matter) may pass them along to the command line invocation of make: > > $ make KCFLAGS=-O3 > > Code that looks to re-add an explicit Kconfig option for `-O3` should > provide: > 1. A rigorous and reproducible performance profile of a reasonable > userspace workload that demonstrates a hot loop in the kernel that > would benefit from `-O3` over `-O2`. > 2. Disassembly of said loop body before and after. > 3. Provides stats on terms of increase in file size. > > Link: https://lore.kernel.org/linux-kbuild/CA+55aFz2sNBbZyg-_i8_Ldr2e8o9dfvdSfHHuRzVtP2VMAUWPg@mail.gmail.com/ > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > --- Applied to linux-kbuild. Thanks. > Makefile | 2 -- > arch/arc/configs/axs101_defconfig | 1 - > arch/arc/configs/axs103_defconfig | 1 - > arch/arc/configs/axs103_smp_defconfig | 1 - > arch/arc/configs/haps_hs_defconfig | 1 - > arch/arc/configs/haps_hs_smp_defconfig | 1 - > arch/arc/configs/hsdk_defconfig | 1 - > arch/arc/configs/nsim_700_defconfig | 1 - > arch/arc/configs/nsimosci_defconfig | 1 - > arch/arc/configs/nsimosci_hs_defconfig | 1 - > arch/arc/configs/nsimosci_hs_smp_defconfig | 1 - > arch/arc/configs/tb10x_defconfig | 1 - > arch/arc/configs/vdk_hs38_defconfig | 1 - > arch/arc/configs/vdk_hs38_smp_defconfig | 1 - > init/Kconfig | 7 ------- > 15 files changed, 22 deletions(-) > > diff --git a/Makefile b/Makefile > index 8973b285ce6c..b69f6cd7f2e2 100644 > --- a/Makefile > +++ b/Makefile > @@ -755,8 +755,6 @@ KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) > > ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE > KBUILD_CFLAGS += -O2 > -else ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 > -KBUILD_CFLAGS += -O3 > else ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE > KBUILD_CFLAGS += -Os > endif > diff --git a/arch/arc/configs/axs101_defconfig b/arch/arc/configs/axs101_defconfig > index 0016149f9583..e31a8ebc3ecc 100644 > --- a/arch/arc/configs/axs101_defconfig > +++ b/arch/arc/configs/axs101_defconfig > @@ -9,7 +9,6 @@ CONFIG_NAMESPACES=y > # CONFIG_UTS_NS is not set > # CONFIG_PID_NS is not set > CONFIG_BLK_DEV_INITRD=y > -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y > CONFIG_EMBEDDED=y > CONFIG_PERF_EVENTS=y > # CONFIG_VM_EVENT_COUNTERS is not set > diff --git a/arch/arc/configs/axs103_defconfig b/arch/arc/configs/axs103_defconfig > index 5b031582a1cf..e0e8567f0d75 100644 > --- a/arch/arc/configs/axs103_defconfig > +++ b/arch/arc/configs/axs103_defconfig > @@ -9,7 +9,6 @@ CONFIG_NAMESPACES=y > # CONFIG_UTS_NS is not set > # CONFIG_PID_NS is not set > CONFIG_BLK_DEV_INITRD=y > -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y > CONFIG_EMBEDDED=y > CONFIG_PERF_EVENTS=y > # CONFIG_VM_EVENT_COUNTERS is not set > diff --git a/arch/arc/configs/axs103_smp_defconfig b/arch/arc/configs/axs103_smp_defconfig > index d4eec39e0112..fcbc952bc75b 100644 > --- a/arch/arc/configs/axs103_smp_defconfig > +++ b/arch/arc/configs/axs103_smp_defconfig > @@ -9,7 +9,6 @@ CONFIG_NAMESPACES=y > # CONFIG_UTS_NS is not set > # CONFIG_PID_NS is not set > CONFIG_BLK_DEV_INITRD=y > -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y > CONFIG_EMBEDDED=y > CONFIG_PERF_EVENTS=y > # CONFIG_VM_EVENT_COUNTERS is not set > diff --git a/arch/arc/configs/haps_hs_defconfig b/arch/arc/configs/haps_hs_defconfig > index 7337cdf4ffdd..d87ad7e88d62 100644 > --- a/arch/arc/configs/haps_hs_defconfig > +++ b/arch/arc/configs/haps_hs_defconfig > @@ -11,7 +11,6 @@ CONFIG_NAMESPACES=y > # CONFIG_UTS_NS is not set > # CONFIG_PID_NS is not set > CONFIG_BLK_DEV_INITRD=y > -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y > CONFIG_EXPERT=y > CONFIG_PERF_EVENTS=y > # CONFIG_COMPAT_BRK is not set > diff --git a/arch/arc/configs/haps_hs_smp_defconfig b/arch/arc/configs/haps_hs_smp_defconfig > index bc927221afc0..8d82cdb7f86a 100644 > --- a/arch/arc/configs/haps_hs_smp_defconfig > +++ b/arch/arc/configs/haps_hs_smp_defconfig > @@ -11,7 +11,6 @@ CONFIG_NAMESPACES=y > # CONFIG_UTS_NS is not set > # CONFIG_PID_NS is not set > CONFIG_BLK_DEV_INITRD=y > -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y > CONFIG_EMBEDDED=y > CONFIG_PERF_EVENTS=y > # CONFIG_VM_EVENT_COUNTERS is not set > diff --git a/arch/arc/configs/hsdk_defconfig b/arch/arc/configs/hsdk_defconfig > index aa000075a575..f856b03e0fb5 100644 > --- a/arch/arc/configs/hsdk_defconfig > +++ b/arch/arc/configs/hsdk_defconfig > @@ -9,7 +9,6 @@ CONFIG_NAMESPACES=y > # CONFIG_PID_NS is not set > CONFIG_BLK_DEV_INITRD=y > CONFIG_BLK_DEV_RAM=y > -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y > CONFIG_EMBEDDED=y > CONFIG_PERF_EVENTS=y > # CONFIG_VM_EVENT_COUNTERS is not set > diff --git a/arch/arc/configs/nsim_700_defconfig b/arch/arc/configs/nsim_700_defconfig > index 326f6cde7826..a1ce12bf5b16 100644 > --- a/arch/arc/configs/nsim_700_defconfig > +++ b/arch/arc/configs/nsim_700_defconfig > @@ -11,7 +11,6 @@ CONFIG_NAMESPACES=y > # CONFIG_UTS_NS is not set > # CONFIG_PID_NS is not set > CONFIG_BLK_DEV_INITRD=y > -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y > CONFIG_KALLSYMS_ALL=y > CONFIG_EMBEDDED=y > CONFIG_PERF_EVENTS=y > diff --git a/arch/arc/configs/nsimosci_defconfig b/arch/arc/configs/nsimosci_defconfig > index bf39a0091679..ca10f4a2c823 100644 > --- a/arch/arc/configs/nsimosci_defconfig > +++ b/arch/arc/configs/nsimosci_defconfig > @@ -10,7 +10,6 @@ CONFIG_NAMESPACES=y > # CONFIG_UTS_NS is not set > # CONFIG_PID_NS is not set > CONFIG_BLK_DEV_INITRD=y > -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y > CONFIG_KALLSYMS_ALL=y > CONFIG_EMBEDDED=y > CONFIG_PERF_EVENTS=y > diff --git a/arch/arc/configs/nsimosci_hs_defconfig b/arch/arc/configs/nsimosci_hs_defconfig > index 7121bd71c543..31b6ec3683c6 100644 > --- a/arch/arc/configs/nsimosci_hs_defconfig > +++ b/arch/arc/configs/nsimosci_hs_defconfig > @@ -10,7 +10,6 @@ CONFIG_NAMESPACES=y > # CONFIG_UTS_NS is not set > # CONFIG_PID_NS is not set > CONFIG_BLK_DEV_INITRD=y > -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y > CONFIG_KALLSYMS_ALL=y > CONFIG_EMBEDDED=y > CONFIG_PERF_EVENTS=y > diff --git a/arch/arc/configs/nsimosci_hs_smp_defconfig b/arch/arc/configs/nsimosci_hs_smp_defconfig > index f9863b294a70..41a0037f48a5 100644 > --- a/arch/arc/configs/nsimosci_hs_smp_defconfig > +++ b/arch/arc/configs/nsimosci_hs_smp_defconfig > @@ -8,7 +8,6 @@ CONFIG_IKCONFIG_PROC=y > # CONFIG_UTS_NS is not set > # CONFIG_PID_NS is not set > CONFIG_BLK_DEV_INITRD=y > -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y > CONFIG_PERF_EVENTS=y > # CONFIG_COMPAT_BRK is not set > CONFIG_KPROBES=y > diff --git a/arch/arc/configs/tb10x_defconfig b/arch/arc/configs/tb10x_defconfig > index a12656ec0072..d93b65008d4a 100644 > --- a/arch/arc/configs/tb10x_defconfig > +++ b/arch/arc/configs/tb10x_defconfig > @@ -14,7 +14,6 @@ CONFIG_INITRAMFS_SOURCE="../tb10x-rootfs.cpio" > CONFIG_INITRAMFS_ROOT_UID=2100 > CONFIG_INITRAMFS_ROOT_GID=501 > # CONFIG_RD_GZIP is not set > -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y > CONFIG_KALLSYMS_ALL=y > # CONFIG_AIO is not set > CONFIG_EMBEDDED=y > diff --git a/arch/arc/configs/vdk_hs38_defconfig b/arch/arc/configs/vdk_hs38_defconfig > index d7c858df520c..0c3b21416819 100644 > --- a/arch/arc/configs/vdk_hs38_defconfig > +++ b/arch/arc/configs/vdk_hs38_defconfig > @@ -4,7 +4,6 @@ CONFIG_HIGH_RES_TIMERS=y > CONFIG_IKCONFIG=y > CONFIG_IKCONFIG_PROC=y > CONFIG_BLK_DEV_INITRD=y > -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y > CONFIG_EMBEDDED=y > CONFIG_PERF_EVENTS=y > # CONFIG_VM_EVENT_COUNTERS is not set > diff --git a/arch/arc/configs/vdk_hs38_smp_defconfig b/arch/arc/configs/vdk_hs38_smp_defconfig > index 015c1d43889e..f9ad9d3ee702 100644 > --- a/arch/arc/configs/vdk_hs38_smp_defconfig > +++ b/arch/arc/configs/vdk_hs38_smp_defconfig > @@ -4,7 +4,6 @@ CONFIG_HIGH_RES_TIMERS=y > CONFIG_IKCONFIG=y > CONFIG_IKCONFIG_PROC=y > CONFIG_BLK_DEV_INITRD=y > -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y > CONFIG_EMBEDDED=y > CONFIG_PERF_EVENTS=y > # CONFIG_VM_EVENT_COUNTERS is not set > diff --git a/init/Kconfig b/init/Kconfig > index c7900e8975f1..1b4d8acc3def 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -1401,13 +1401,6 @@ config CC_OPTIMIZE_FOR_PERFORMANCE > with the "-O2" compiler flag for best performance and most > helpful compile-time warnings. > > -config CC_OPTIMIZE_FOR_PERFORMANCE_O3 > - bool "Optimize more for performance (-O3)" > - depends on ARC > - help > - Choosing this option will pass "-O3" to your compiler to optimize > - the kernel yet more for performance. > - > config CC_OPTIMIZE_FOR_SIZE > bool "Optimize for size (-Os)" > help > -- > 2.37.0.rc0.161.g10f37bed90-goog >
On Wed, Jun 29, 2022 at 7:48 PM Miko Larsson <mikoxyzzz@gmail.com> wrote: > > On Tuesday, 28 June 2022 23:04:07 CEST Nick Desaulniers wrote: > > The difference in most compilers between `-O3` and `-O2` is mostly down > > to whether loops with statically determinable trip counts are fully > > unrolled vs unrolled to a multiple of SIMD width. > > > > This patch is effectively a revert of > > commit 15f5db60a137 ("kbuild,arc: add > > CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 for ARC") without re-adding > > ARCH_CFLAGS > > > > Ever since > > commit cfdbc2e16e65 ("ARC: Build system: Makefiles, Kconfig, Linker > > script") > > ARC has been built with -O3, though the reason for doing so was not > > specified in inline comments or the commit message. This commit does not > > re-add -O3 to arch/arc/Makefile. > > > > Folks looking to experiment with `-O3` (or any compiler flag for that > > matter) may pass them along to the command line invocation of make: > > > > $ make KCFLAGS=-O3 > > > > Code that looks to re-add an explicit Kconfig option for `-O3` should > > provide: > > 1. A rigorous and reproducible performance profile of a reasonable > > userspace workload that demonstrates a hot loop in the kernel that > > would benefit from `-O3` over `-O2`. > > 2. Disassembly of said loop body before and after. > > 3. Provides stats on terms of increase in file size. > > > > Might be worth cleaning up the rest of the kernel of instances of -O3, > too. -O3 used to build lz4 and mips vdso, for instance. Might be a bit > of a digression, though This patch focuses on the removal of CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3, so I think it is OK as-is. The rest of cleanups, if needed, should be submitted separately. > > -- > ~miko > >
diff --git a/Makefile b/Makefile index 8973b285ce6c..b69f6cd7f2e2 100644 --- a/Makefile +++ b/Makefile @@ -755,8 +755,6 @@ KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE KBUILD_CFLAGS += -O2 -else ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 -KBUILD_CFLAGS += -O3 else ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE KBUILD_CFLAGS += -Os endif diff --git a/arch/arc/configs/axs101_defconfig b/arch/arc/configs/axs101_defconfig index 0016149f9583..e31a8ebc3ecc 100644 --- a/arch/arc/configs/axs101_defconfig +++ b/arch/arc/configs/axs101_defconfig @@ -9,7 +9,6 @@ CONFIG_NAMESPACES=y # CONFIG_UTS_NS is not set # CONFIG_PID_NS is not set CONFIG_BLK_DEV_INITRD=y -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y CONFIG_EMBEDDED=y CONFIG_PERF_EVENTS=y # CONFIG_VM_EVENT_COUNTERS is not set diff --git a/arch/arc/configs/axs103_defconfig b/arch/arc/configs/axs103_defconfig index 5b031582a1cf..e0e8567f0d75 100644 --- a/arch/arc/configs/axs103_defconfig +++ b/arch/arc/configs/axs103_defconfig @@ -9,7 +9,6 @@ CONFIG_NAMESPACES=y # CONFIG_UTS_NS is not set # CONFIG_PID_NS is not set CONFIG_BLK_DEV_INITRD=y -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y CONFIG_EMBEDDED=y CONFIG_PERF_EVENTS=y # CONFIG_VM_EVENT_COUNTERS is not set diff --git a/arch/arc/configs/axs103_smp_defconfig b/arch/arc/configs/axs103_smp_defconfig index d4eec39e0112..fcbc952bc75b 100644 --- a/arch/arc/configs/axs103_smp_defconfig +++ b/arch/arc/configs/axs103_smp_defconfig @@ -9,7 +9,6 @@ CONFIG_NAMESPACES=y # CONFIG_UTS_NS is not set # CONFIG_PID_NS is not set CONFIG_BLK_DEV_INITRD=y -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y CONFIG_EMBEDDED=y CONFIG_PERF_EVENTS=y # CONFIG_VM_EVENT_COUNTERS is not set diff --git a/arch/arc/configs/haps_hs_defconfig b/arch/arc/configs/haps_hs_defconfig index 7337cdf4ffdd..d87ad7e88d62 100644 --- a/arch/arc/configs/haps_hs_defconfig +++ b/arch/arc/configs/haps_hs_defconfig @@ -11,7 +11,6 @@ CONFIG_NAMESPACES=y # CONFIG_UTS_NS is not set # CONFIG_PID_NS is not set CONFIG_BLK_DEV_INITRD=y -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y CONFIG_EXPERT=y CONFIG_PERF_EVENTS=y # CONFIG_COMPAT_BRK is not set diff --git a/arch/arc/configs/haps_hs_smp_defconfig b/arch/arc/configs/haps_hs_smp_defconfig index bc927221afc0..8d82cdb7f86a 100644 --- a/arch/arc/configs/haps_hs_smp_defconfig +++ b/arch/arc/configs/haps_hs_smp_defconfig @@ -11,7 +11,6 @@ CONFIG_NAMESPACES=y # CONFIG_UTS_NS is not set # CONFIG_PID_NS is not set CONFIG_BLK_DEV_INITRD=y -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y CONFIG_EMBEDDED=y CONFIG_PERF_EVENTS=y # CONFIG_VM_EVENT_COUNTERS is not set diff --git a/arch/arc/configs/hsdk_defconfig b/arch/arc/configs/hsdk_defconfig index aa000075a575..f856b03e0fb5 100644 --- a/arch/arc/configs/hsdk_defconfig +++ b/arch/arc/configs/hsdk_defconfig @@ -9,7 +9,6 @@ CONFIG_NAMESPACES=y # CONFIG_PID_NS is not set CONFIG_BLK_DEV_INITRD=y CONFIG_BLK_DEV_RAM=y -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y CONFIG_EMBEDDED=y CONFIG_PERF_EVENTS=y # CONFIG_VM_EVENT_COUNTERS is not set diff --git a/arch/arc/configs/nsim_700_defconfig b/arch/arc/configs/nsim_700_defconfig index 326f6cde7826..a1ce12bf5b16 100644 --- a/arch/arc/configs/nsim_700_defconfig +++ b/arch/arc/configs/nsim_700_defconfig @@ -11,7 +11,6 @@ CONFIG_NAMESPACES=y # CONFIG_UTS_NS is not set # CONFIG_PID_NS is not set CONFIG_BLK_DEV_INITRD=y -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y CONFIG_KALLSYMS_ALL=y CONFIG_EMBEDDED=y CONFIG_PERF_EVENTS=y diff --git a/arch/arc/configs/nsimosci_defconfig b/arch/arc/configs/nsimosci_defconfig index bf39a0091679..ca10f4a2c823 100644 --- a/arch/arc/configs/nsimosci_defconfig +++ b/arch/arc/configs/nsimosci_defconfig @@ -10,7 +10,6 @@ CONFIG_NAMESPACES=y # CONFIG_UTS_NS is not set # CONFIG_PID_NS is not set CONFIG_BLK_DEV_INITRD=y -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y CONFIG_KALLSYMS_ALL=y CONFIG_EMBEDDED=y CONFIG_PERF_EVENTS=y diff --git a/arch/arc/configs/nsimosci_hs_defconfig b/arch/arc/configs/nsimosci_hs_defconfig index 7121bd71c543..31b6ec3683c6 100644 --- a/arch/arc/configs/nsimosci_hs_defconfig +++ b/arch/arc/configs/nsimosci_hs_defconfig @@ -10,7 +10,6 @@ CONFIG_NAMESPACES=y # CONFIG_UTS_NS is not set # CONFIG_PID_NS is not set CONFIG_BLK_DEV_INITRD=y -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y CONFIG_KALLSYMS_ALL=y CONFIG_EMBEDDED=y CONFIG_PERF_EVENTS=y diff --git a/arch/arc/configs/nsimosci_hs_smp_defconfig b/arch/arc/configs/nsimosci_hs_smp_defconfig index f9863b294a70..41a0037f48a5 100644 --- a/arch/arc/configs/nsimosci_hs_smp_defconfig +++ b/arch/arc/configs/nsimosci_hs_smp_defconfig @@ -8,7 +8,6 @@ CONFIG_IKCONFIG_PROC=y # CONFIG_UTS_NS is not set # CONFIG_PID_NS is not set CONFIG_BLK_DEV_INITRD=y -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y CONFIG_PERF_EVENTS=y # CONFIG_COMPAT_BRK is not set CONFIG_KPROBES=y diff --git a/arch/arc/configs/tb10x_defconfig b/arch/arc/configs/tb10x_defconfig index a12656ec0072..d93b65008d4a 100644 --- a/arch/arc/configs/tb10x_defconfig +++ b/arch/arc/configs/tb10x_defconfig @@ -14,7 +14,6 @@ CONFIG_INITRAMFS_SOURCE="../tb10x-rootfs.cpio" CONFIG_INITRAMFS_ROOT_UID=2100 CONFIG_INITRAMFS_ROOT_GID=501 # CONFIG_RD_GZIP is not set -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y CONFIG_KALLSYMS_ALL=y # CONFIG_AIO is not set CONFIG_EMBEDDED=y diff --git a/arch/arc/configs/vdk_hs38_defconfig b/arch/arc/configs/vdk_hs38_defconfig index d7c858df520c..0c3b21416819 100644 --- a/arch/arc/configs/vdk_hs38_defconfig +++ b/arch/arc/configs/vdk_hs38_defconfig @@ -4,7 +4,6 @@ CONFIG_HIGH_RES_TIMERS=y CONFIG_IKCONFIG=y CONFIG_IKCONFIG_PROC=y CONFIG_BLK_DEV_INITRD=y -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y CONFIG_EMBEDDED=y CONFIG_PERF_EVENTS=y # CONFIG_VM_EVENT_COUNTERS is not set diff --git a/arch/arc/configs/vdk_hs38_smp_defconfig b/arch/arc/configs/vdk_hs38_smp_defconfig index 015c1d43889e..f9ad9d3ee702 100644 --- a/arch/arc/configs/vdk_hs38_smp_defconfig +++ b/arch/arc/configs/vdk_hs38_smp_defconfig @@ -4,7 +4,6 @@ CONFIG_HIGH_RES_TIMERS=y CONFIG_IKCONFIG=y CONFIG_IKCONFIG_PROC=y CONFIG_BLK_DEV_INITRD=y -CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y CONFIG_EMBEDDED=y CONFIG_PERF_EVENTS=y # CONFIG_VM_EVENT_COUNTERS is not set diff --git a/init/Kconfig b/init/Kconfig index c7900e8975f1..1b4d8acc3def 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1401,13 +1401,6 @@ config CC_OPTIMIZE_FOR_PERFORMANCE with the "-O2" compiler flag for best performance and most helpful compile-time warnings. -config CC_OPTIMIZE_FOR_PERFORMANCE_O3 - bool "Optimize more for performance (-O3)" - depends on ARC - help - Choosing this option will pass "-O3" to your compiler to optimize - the kernel yet more for performance. - config CC_OPTIMIZE_FOR_SIZE bool "Optimize for size (-Os)" help
The difference in most compilers between `-O3` and `-O2` is mostly down to whether loops with statically determinable trip counts are fully unrolled vs unrolled to a multiple of SIMD width. This patch is effectively a revert of commit 15f5db60a137 ("kbuild,arc: add CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 for ARC") without re-adding ARCH_CFLAGS Ever since commit cfdbc2e16e65 ("ARC: Build system: Makefiles, Kconfig, Linker script") ARC has been built with -O3, though the reason for doing so was not specified in inline comments or the commit message. This commit does not re-add -O3 to arch/arc/Makefile. Folks looking to experiment with `-O3` (or any compiler flag for that matter) may pass them along to the command line invocation of make: $ make KCFLAGS=-O3 Code that looks to re-add an explicit Kconfig option for `-O3` should provide: 1. A rigorous and reproducible performance profile of a reasonable userspace workload that demonstrates a hot loop in the kernel that would benefit from `-O3` over `-O2`. 2. Disassembly of said loop body before and after. 3. Provides stats on terms of increase in file size. Link: https://lore.kernel.org/linux-kbuild/CA+55aFz2sNBbZyg-_i8_Ldr2e8o9dfvdSfHHuRzVtP2VMAUWPg@mail.gmail.com/ Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> --- Makefile | 2 -- arch/arc/configs/axs101_defconfig | 1 - arch/arc/configs/axs103_defconfig | 1 - arch/arc/configs/axs103_smp_defconfig | 1 - arch/arc/configs/haps_hs_defconfig | 1 - arch/arc/configs/haps_hs_smp_defconfig | 1 - arch/arc/configs/hsdk_defconfig | 1 - arch/arc/configs/nsim_700_defconfig | 1 - arch/arc/configs/nsimosci_defconfig | 1 - arch/arc/configs/nsimosci_hs_defconfig | 1 - arch/arc/configs/nsimosci_hs_smp_defconfig | 1 - arch/arc/configs/tb10x_defconfig | 1 - arch/arc/configs/vdk_hs38_defconfig | 1 - arch/arc/configs/vdk_hs38_smp_defconfig | 1 - init/Kconfig | 7 ------- 15 files changed, 22 deletions(-)