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Uros Bizjak
da3f52ba35
Use atomic64_try_cmpxchg instead of
atomic64_cmpxchg (*ptr, old, new) == old in inode_set_max_iversion_raw,
inode_maybe_inc_version and inode_query_iversion. x86 CMPXCHG instruction
returns success in ZF flag, so this change saves a compare after cmpxchg
(and related move instruction in front of cmpxchg).
Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails, enabling further code simplifications.
The loop in inode_maybe_inc_iversion improves from:
5563: 48 89 ca mov %rcx,%rdx
5566: 48 89 c8 mov %rcx,%rax
5569: 48 83 e2 fe and $0xfffffffffffffffe,%rdx
556d: 48 83 c2 02 add $0x2,%rdx
5571: f0 48 0f b1 16 lock cmpxchg %rdx,(%rsi)
5576: 48 39 c1 cmp %rax,%rcx
5579: 0f 84 85 fc ff ff je 5204 <...>
557f: 48 89 c1 mov %rax,%rcx
5582: eb df jmp 5563 <...>
to:
5563: 48 89 c2 mov %rax,%rdx
5566: 48 83 e2 fe and $0xfffffffffffffffe,%rdx
556a: 48 83 c2 02 add $0x2,%rdx
556e: f0 48 0f b1 11 lock cmpxchg %rdx,(%rcx)
5573: 0f 84 8b fc ff ff je 5204 <...>
5579: eb e8 jmp 5563 <...>
Link: https://lkml.kernel.org/r/20220821193011.88208-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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.