On Wed, Jun 29, 2022 at 6:06 AM 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.
>
> Link:
> https://lore.kernel.org/linux-kbuild/ca+55afz2snbbzyg-_i8_ldr2e8o9dfvdsfhhurzvtp2vmau...@mail.gmail.com/
> Signed-off-by: Nick Desaulniers
> ---
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
