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Mark Rutland 16860a209c arm64: atomics: remove redundant static branch 
Due to a historical oversight, we emit a redundant static branch for
each atomic/atomic64 operation when CONFIG_ARM64_LSE_ATOMICS is
selected. We can safely remove this, making the kernel Image reasonably
smaller.

When CONFIG_ARM64_LSE_ATOMICS is selected, every LSE atomic operation
has two preceding static branches with the same target, e.g.

	b	f7c <kernel_init_freeable+0xa4>
	b	f7c <kernel_init_freeable+0xa4>
	mov	w0, #0x1                   	// #1
	ldadd	w0, w0, [x19]

This is because the __lse_ll_sc_body() wrapper uses
system_uses_lse_atomics(), which checks both `arm64_const_caps_ready`
and `cpu_hwcap_keys[ARM64_HAS_LSE_ATOMICS]`, each of which emits a
static branch. This has been the case since commit:

  addfc38672 ("arm64: atomics: avoid out-of-line ll/sc atomics")

However, there was never a need to check `arm64_const_caps_ready`, which
was itself introduced in commit:

  63a1e1c95e ("arm64/cpufeature: don't use mutex in bringup path")

... so that cpus_have_const_cap() could fall back to checking the
`cpu_hwcaps` bitmap prior to the static keys for individual caps
becoming enabled. As system_uses_lse_atomics() doesn't check
`cpu_hwcaps`, and doesn't need to as we can safely use the LL/SC atomics
prior to enabling the `ARM64_HAS_LSE_ATOMICS` static key, it doesn't
need to check `arm64_const_caps_ready`.

This patch removes the `arm64_const_caps_ready` check from
system_uses_lse_atomics(). As the arch_atomic_* routines are meant to be
safely usable in noinstr code, I've also marked
system_uses_lse_atomics() as __always_inline.

This results in one fewer static branch per atomic operation, with the
prior example becoming:

	b	f78 <kernel_init_freeable+0xa0>
	mov	w0, #0x1                   	// #1
	ldadd	w0, w0, [x19]

Each static branch consists of the branch itself and an associated
__jump_table entry. Removing these has a reasonable impact on the Image
size, with a GCC 11.1.0 defconfig v5.17-rc2 Image being reduced by
128KiB:

| [mark@lakrids:~/src/linux]% ls -al Image*
| -rw-r--r-- 1 mark mark 34619904 Feb  3 18:24 Image.baseline
| -rw-r--r-- 1 mark mark 34488832 Feb  3 18:33 Image.onebranch

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Suzuki Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20220204104439.270567-1-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
History 2022-02-15 17:54:08 +00:00
arch arm64: atomics: remove redundant static branch 2022-02-15 17:54:08 +00:00
block block: bio-integrity: Advance seed correctly for larger interval sizes 2022-02-03 21:09:24 -07:00
certs certs: Fix build error when CONFIG_MODULE_SIG_KEY is empty 2022-01-23 00:08:44 +09:00
crypto lib/crypto: blake2s: avoid indirect calls to compression function for Clang CFI 2022-02-04 19:22:32 +01:00
Documentation xen: branch for v5.17-rc3 2022-02-05 10:40:17 -08:00
drivers - Remove a bogus warning introduced by the recent PCI MSI irq affinity 2022-02-06 10:00:40 -08:00
fs Various bug fixes for ext4 fast commit and inline data handling. Also 2022-02-06 10:34:45 -08:00
include Various bug fixes for ext4 fast commit and inline data handling. Also 2022-02-06 10:34:45 -08:00
init lib/stackdepot: allow optional init and stack_table allocation by kvmalloc() 2022-01-22 08:33:37 +02:00
ipc ipc/sem: do not sleep with a spin lock held 2022-02-04 09:25:05 -08:00
kernel perf/urgent contains 3 fixups: 2022-02-06 10:11:14 -08:00
lib lib/crypto: blake2s: avoid indirect calls to compression function for Clang CFI 2022-02-04 19:22:32 +01:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm/kmemleak: avoid scanning potential huge holes 2022-02-04 09:25:05 -08:00
net A patch to make it possible to disable zero copy path in the messenger 2022-02-04 09:54:02 -08:00
samples Merge branch 'akpm' (patches from Andrew) 2022-01-20 10:41:01 +02:00
scripts ftrace: Have architectures opt-in for mcount build time sorting 2022-01-27 19:15:44 -05:00
security selinux/stable-5.17 PR 20220203 2022-02-03 16:44:12 -08:00
sound ASoC: Fixes for v5.17 2022-02-01 16:52:54 +01:00
tools perf tools fixes for v5.17: 1st batch 2022-02-06 10:18:23 -08:00
usr kbuild: remove include/linux/cyclades.h from header file check 2022-01-27 08:51:08 +01:00
virt Two larger x86 series: 2022-01-28 19:00:26 +02:00
.clang-format genirq/msi: Make interrupt allocation less convoluted 2021-12-16 22:22:20 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.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 .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: update Christian Brauner's email address 2022-02-01 11:21:31 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Removing Ohad from remoteproc/rpmsg maintenance 2021-12-08 10:09:40 -07:00
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 ata fixes for 5.17-rc3 2022-02-04 11:52:37 -08:00
Makefile Linux 5.17-rc3 2022-02-06 12:20:50 -08:00
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.