kbuild: drop support for CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3

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>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

diff --git a/Makefile b/Makefile
index faa4880f25f7e8e81ac2872d8ec0c3ddff3db4c8..f8e325709bf37e2bd6321822a757a07b598d2648 100644 (file)
--- 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 0016149f958304a2420817650846eb4eafec81bd..e31a8ebc3eccb0b628f71ea86d6632976154f360 100644 (file)
--- 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 5b031582a1cf8bad73f836f02d47380e6a557083..e0e8567f0d7585587ff4eee641f0fc814c8b1c77 100644 (file)
--- 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 d4eec39e0112c4e8511a046b64f05ea20dc417c3..fcbc952bc75bb973a941a829dad2db4443c0d824 100644 (file)
--- 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 7337cdf4ffddab362be9021adb7e83032ec84fab..d87ad7e88d624a09b8b9ec43f02ca1fad2942870 100644 (file)
--- 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 bc927221afc0e02ad95fe753893de18ac9141d42..8d82cdb7f86a6ac6619c4e6e2a50a53d379d9704 100644 (file)
--- 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 aa000075a575744427c42f2399e87b5eced91277..f856b03e0fb5cd42e8e8d161c0efe7ad41e87be8 100644 (file)
--- 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 326f6cde7826895b9553b13d0ea3d4969a7c3662..a1ce12bf5b1659c2f932012abbba69b78c1ae7d4 100644 (file)
--- 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 bf39a0091679c766fa54f7670b4d351bf50dc6c8..ca10f4a2c823fb370c7a70f5cda625ce047962a3 100644 (file)
--- 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 7121bd71c543ad3232e2ca97eb01a7ddda1e9921..31b6ec3683c65beedb5e60bf81a04a4e8b80616a 100644 (file)
--- 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 f9863b294a707ef569bf36aa08592bf8ca48b5f2..41a0037f48a58a0c85b3d25a80af9531fb34b970 100644 (file)
--- 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 a12656ec00720e1069ca97f85dd1c83a355d0b92..d93b65008d4afdc93f5826c993bbfe0816a0c732 100644 (file)
--- 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 d7c858df520cc07a0e22c8e3f0777356274d7002..0c3b214168197d1c709e4f428d4d02a4b93d4a5a 100644 (file)
--- 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 015c1d43889e6937073f3014cae500f372667091..f9ad9d3ee702d961da37d09f8c697175ce764d33 100644 (file)
--- 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 c7900e8975f181857840d861e1cddd4e8201ecc4..1b4d8acc3def049db8decf1dde91a2b889264a17 100644 (file)
--- 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