locking/atomic/x86: Introduce arch_try_cmpxchg64() for !CONFIG_X86_CMPXCHG64
Commit: 6d12c8d3 ("percpu: Wire up cmpxchg128") improved emulated cmpxchg8b_emu() library function to return success/failure in a ZF flag. Define arch_try_cmpxchg64() for !CONFIG_X86_CMPXCHG64 targets to override the generic archy_try_cmpxchg() with an optimized target specific implementation that handles ZF flag. The assembly code at the call sites improves from: bf56d: e8 fc ff ff ff call cmpxchg8b_emu bf572: 8b 74 24 28 mov 0x28(%esp),%esi bf576: 89 c3 mov %eax,%ebx bf578: 89 d1 mov %edx,%ecx bf57a: 8b 7c 24 2c mov 0x2c(%esp),%edi bf57e: 89 f0 mov %esi,%eax bf580: 89 fa mov %edi,%edx bf582: 31 d8 xor %ebx,%eax bf584: 31 ca xor %ecx,%edx bf586: 09 d0 or %edx,%eax bf588: 0f 84 e3 01 00 00 je bf771 <...> to: bf572: e8 fc ff ff ff call cmpxchg8b_emu bf577: 0f 84 b6 01 00 00 je bf733 <...> Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: "H. Peter Anvin" <hpa@zytor.com> Link: https://lore.kernel.org/r/20240408091547.90111-4-ubizjak@gmail.com
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