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5259401ef8
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Alexander Lobakin 5259401ef8 bitops: let the compiler optimize {__,}assign_bit() 
Since commit b03fc1173c ("bitops: let optimize out non-atomic bitops
on compile-time constants"), the compilers are able to expand inline
bitmap operations to compile-time initializers when possible.
However, during the round of replacement if-__set-else-__clear with
__assign_bit() as per Andy's advice, bloat-o-meter showed +1024 bytes
difference in object code size for one module (even one function),
where the pattern:

	DECLARE_BITMAP(foo) = { }; // on the stack, zeroed

	if (a)
		__set_bit(const_bit_num, foo);
	if (b)
		__set_bit(another_const_bit_num, foo);
	...

is heavily used, although there should be no difference: the bitmap is
zeroed, so the second half of __assign_bit() should be compiled-out as
a no-op.
I either missed the fact that __assign_bit() has bitmap pointer marked
as `volatile` (as we usually do for bitops) or was hoping that the
compilers would at least try to look past the `volatile` for
__always_inline functions. Anyhow, due to that attribute, the compilers
were always compiling the whole expression and no mentioned compile-time
optimizations were working.

Convert __assign_bit() to a macro since it's a very simple if-else and
all of the checks are performed inside __set_bit() and __clear_bit(),
thus that wrapper has to be as transparent as possible. After that
change, despite it showing only -20 bytes change for vmlinux (due to
that it's still relatively unpopular), no drastic code size changes
happen when replacing if-set-else-clear for onstack bitmaps with
__assign_bit(), meaning the compiler now expands them to the actual
operations will all the expected optimizations.

Atomic assign_bit() is less affected due to its nature, but let's
convert it to a macro as well to keep the code consistent and not
leave a place for possible suboptimal codegen. Moreover, with certain
kernel configuration it actually gives some saves (x86):

do_ip_setsockopt    4154    4099     -55

Suggested-by: Yury Norov <yury.norov@gmail.com> # assign_bit(), too
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Acked-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2024-04-01 10:49:27 +01:00
arch Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2024-03-28 17:25:57 -07:00
block vfs-6.9-rc1.fixes 2024-03-18 09:15:50 -07:00
certs This update includes the following changes: 2023-11-02 16:15:30 -10:00
crypto net: add sk_wake_async_rcu() helper 2024-03-29 15:03:11 -07:00
Documentation dt-bindings: net: dwmac: Document STM32 property st,ext-phyclk 2024-03-29 15:42:11 -07:00
drivers netlink: introduce type-checking attribute iteration 2024-03-29 15:06:02 -07:00
fs Changes since last update: 2024-03-27 20:24:09 -07:00
include bitops: let the compiler optimize {__,}assign_bit() 2024-04-01 10:49:27 +01:00
init init: open /initrd.image with O_LARGEFILE 2024-03-26 11:07:19 -07:00
io_uring io_uring/sqpoll: early exit thread if task_context wasn't allocated 2024-03-18 20:22:42 -06:00
ipc sysctl changes for v6.9-rc1 2024-03-18 14:59:13 -07:00
kernel bitops: make BYTES_TO_BITS() treewide-available 2024-04-01 10:49:27 +01:00
lib lib/test_bitmap: use pr_info() for non-error messages 2024-04-01 10:49:27 +01:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm: zswap: fix data loss on SWP_SYNCHRONOUS_IO devices 2024-03-26 11:14:12 -07:00
net netlink: introduce type-checking attribute iteration 2024-03-29 15:06:02 -07:00
rust Kbuild updates for v6.9 2024-03-21 14:41:00 -07:00
samples Tracing updates for 6.9: 2024-03-18 15:11:44 -07:00
scripts compiler_types: add Endianness-dependent __counted_by_{le,be} 2024-03-28 18:50:47 -07:00
security - Kuan-Wei Chiu has developed the well-named series "lib min_heap: Min 2024-03-14 18:03:09 -07:00
sound sound fixes #2 for 6.9-rc2 2024-03-22 09:44:19 -07:00
tools bitops: make BYTES_TO_BITS() treewide-available 2024-04-01 10:49:27 +01:00
usr Kbuild updates for v6.8 2024-01-18 17:57:07 -08:00
virt KVM Xen and pfncache changes for 6.9: 2024-03-11 10:42:55 -04:00
.clang-format clang-format: Update with v6.7-rc4's for_each macro list 2023-12-08 23:54:38 +01:00
.cocciconfig
.editorconfig Add .editorconfig file for basic formatting 2023-12-28 16:22:47 +09:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: create a list of all built DTB files 2024-02-19 18:20:39 +09:00
.mailmap Including fixes from bpf, WiFi and netfilter. 2024-03-28 13:09:37 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS Not a ton of stuff happening in the clk framework in this pull request. We got 2024-03-15 11:48:01 -07:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Including fixes from bpf, WiFi and netfilter. 2024-03-28 13:09:37 -07:00
Makefile Linux 6.9-rc1 2024-03-24 14:10:05 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -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 reStructuredText 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.