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c2df0a6af1
Introduce arch_try_cmpxchg64 for 64-bit and 32-bit targets to improve code using cmpxchg64. On 64-bit targets, the generated assembly improves from: ab: 89 c8 mov %ecx,%eax ad: 48 89 4c 24 60 mov %rcx,0x60(%rsp) b2: 83 e0 fd and $0xfffffffd,%eax b5: 89 54 24 64 mov %edx,0x64(%rsp) b9: 88 44 24 60 mov %al,0x60(%rsp) bd: 48 89 c8 mov %rcx,%rax c0: c6 44 24 62 f2 movb $0xf2,0x62(%rsp) c5: 48 8b 74 24 60 mov 0x60(%rsp),%rsi ca: f0 49 0f b1 34 24 lock cmpxchg %rsi,(%r12) d0: 48 39 c1 cmp %rax,%rcx d3: 75 cf jne a4 <t+0xa4> to: b3: 89 c2 mov %eax,%edx b5: 48 89 44 24 60 mov %rax,0x60(%rsp) ba: 83 e2 fd and $0xfffffffd,%edx bd: 89 4c 24 64 mov %ecx,0x64(%rsp) c1: 88 54 24 60 mov %dl,0x60(%rsp) c5: c6 44 24 62 f2 movb $0xf2,0x62(%rsp) ca: 48 8b 54 24 60 mov 0x60(%rsp),%rdx cf: f0 48 0f b1 13 lock cmpxchg %rdx,(%rbx) d4: 75 d5 jne ab <t+0xab> where a move and a compare after cmpxchg is saved. The improvements for 32-bit targets are even more noticeable, because dual-word compare after cmpxchg8b gets eliminated. Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20220515184205.103089-3-ubizjak@gmail.com
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.