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Uros Bizjak d26e46f6bf locking/atomic/x86: Introduce arch_try_cmpxchg64_local()
Introduce arch_try_cmpxchg64_local() for 64-bit and 32-bit targets
to improve code using cmpxchg64_local().  On 64-bit targets, the
generated assembly improves from:

    3e28:	31 c0                	xor    %eax,%eax
    3e2a:	4d 0f b1 7d 00       	cmpxchg %r15,0x0(%r13)
    3e2f:	48 85 c0             	test   %rax,%rax
    3e32:	0f 85 9f 00 00 00    	jne    3ed7 <...>

to:

    3e28:	31 c0                	xor    %eax,%eax
    3e2a:	4d 0f b1 7d 00       	cmpxchg %r15,0x0(%r13)
    3e2f:	0f 85 9f 00 00 00    	jne    3ed4 <...>

where a TEST instruction after CMPXCHG is saved.  The improvements
for 32-bit targets are even more noticeable, because double-word
compare after CMPXCHG8B gets eliminated.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20240414161257.49145-1-ubizjak@gmail.com
History 2024-04-14 22:40:54 +02:00
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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.