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Nick Desaulniers a6036a41bf 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 15f5db60a1 ("kbuild,arc: add
CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 for ARC") without re-adding
ARCH_CFLAGS

Ever since
commit cfdbc2e16e ("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>
2022-07-27 21:17:59 +09:00
arch kbuild: drop support for CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 2022-07-27 21:17:59 +09:00
block block: remove WARN_ON() from bd_link_disk_holder 2022-06-23 07:48:05 -06:00
certs certs: unify blacklist_hashes.c and blacklist_nohashes.c 2022-07-27 21:17:59 +09:00
crypto crypto: s390 - do not depend on CRYPTO_HW for SIMD implementations 2022-07-06 20:04:06 -07:00
Documentation dmaengine fixes for v5.19 2022-07-10 11:23:01 -07:00
drivers Merge branch 'hot-fixes' (fixes for rc6) 2022-07-10 14:26:49 -07:00
fs o_uring-5.19-2022-07-09 2022-07-10 09:14:54 -07:00
include Char/Misc driver fixes for 5.19-rc6 2022-07-10 09:45:29 -07:00
init kbuild: drop support for CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 2022-07-27 21:17:59 +09:00
ipc These changes update the ipc sysctls so that they are fundamentally 2022-06-03 15:54:57 -07:00
kernel ptrace: fix clearing of JOBCTL_TRACED in ptrace_unfreeze_traced() 2022-07-09 11:06:19 -07:00
lib ida: don't use BUG_ON() for debugging 2022-07-10 13:55:49 -07:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm Minor things, mainly - mailmap updates, MAINTAINERS updates, etc. 2022-06-26 14:00:55 -07:00
net Networking fixes for 5.19-rc6, including fixes from bpf, netfilter, 2022-07-07 10:08:20 -07:00
samples fprobe, samples: Add module parameter descriptions 2022-06-24 15:23:04 -07:00
scripts kbuild: remove sed command from cmd_ar_builtin 2022-07-27 21:17:59 +09:00
security selinux: free contexts previously transferred in selinux_add_opt() 2022-06-15 21:20:45 -04:00
sound ALSA: cs46xx: Fix missing snd_card_free() call at probe error 2022-07-05 17:24:05 +02:00
tools - Prepare for and clear .brk early in order to address XenPV guests 2022-07-10 08:43:52 -07:00
usr Not a lot of material this cycle. Many singleton patches against various 2022-05-27 11:22:03 -07:00
virt KVM: x86: disable preemption around the call to kvm_arch_vcpu_{un|}blocking 2022-06-09 10:52:20 -04:00
.clang-format clang-format: Fix space after for_each macros 2022-05-20 19:27:16 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore kbuild: split the second line of *.mod into *.usyms 2022-05-08 03:16:59 +09:00
.mailmap cxl fixes for 5.19-rc6 2022-07-08 12:55:25 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: replace a Microchip AT91 maintainer 2022-02-09 11:30:01 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS certs: move scripts/check-blacklist-hashes.awk to certs/ 2022-07-27 21:17:59 +09:00
Makefile kbuild: drop support for CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 2022-07-27 21:17:59 +09:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.