Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Subject | [PATCH v2] locking/lockref/x86: Enable ARCH_USE_CMPXCHG_LOCKREF for X86_CMPXCHG64 | Date | Thu, 26 May 2022 20:54:30 +0200 |
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Commit bc08b449ee14ace4d869adaa1bb35a44ce68d775 enabled lockless reference count updates using cmpxchg() only for x86_64 and left x86_32 behind due to inability to detect support for cmpxchg8b instruction. Nowadays, we can use CONFIG_X86_CMPXCHG64 for this purpose. Also, by using try_cmpxchg64() instead of cmpxchg() in CMPXCHG_LOOP macro, the compiler actually produces sane code, improving lockref_get_or_lock main loop from:
2a5: 8d 48 01 lea 0x1(%eax),%ecx 2a8: 85 c0 test %eax,%eax 2aa: 7e 3c jle 2e8 <lockref_get_or_lock+0x78> 2ac: 8b 44 24 08 mov 0x8(%esp),%eax 2b0: 8b 54 24 0c mov 0xc(%esp),%edx 2b4: 8b 74 24 04 mov 0x4(%esp),%esi 2b8: f0 0f c7 0e lock cmpxchg8b (%esi) 2bc: 8b 4c 24 0c mov 0xc(%esp),%ecx 2c0: 89 c3 mov %eax,%ebx 2c2: 89 d0 mov %edx,%eax 2c4: 8b 74 24 08 mov 0x8(%esp),%esi 2c8: 31 ca xor %ecx,%edx 2ca: 31 de xor %ebx,%esi 2cc: 09 f2 or %esi,%edx 2ce: 75 40 jne 310 <lockref_get_or_lock+0xa0>
to:
2d: 8d 4f 01 lea 0x1(%edi),%ecx 30: 85 ff test %edi,%edi 32: 7e 1c jle 50 <lockref_get_or_lock+0x50> 34: f0 0f c7 0e lock cmpxchg8b (%esi) 38: 75 36 jne 70 <lockref_get_or_lock+0x70>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> --- v2: - select ARCH_USE_CMPXCHG_LOCKREF for CONFIG_X86_CMPXCHG which is unconditionally defined for X86_64 --- arch/x86/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 6f59517c4356..cfc42f370419 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -27,7 +27,6 @@ config X86_64 # Options that are inherently 64-bit kernel only: select ARCH_HAS_GIGANTIC_PAGE select ARCH_SUPPORTS_INT128 if CC_HAS_INT128 - select ARCH_USE_CMPXCHG_LOCKREF select HAVE_ARCH_SOFT_DIRTY select MODULES_USE_ELF_RELA select NEED_DMA_MAP_STATE @@ -111,6 +110,7 @@ config X86 select ARCH_SUPPORTS_LTO_CLANG select ARCH_SUPPORTS_LTO_CLANG_THIN select ARCH_USE_BUILTIN_BSWAP + select ARCH_USE_CMPXCHG_LOCKREF if X86_CMPXCHG64 select ARCH_USE_MEMTEST select ARCH_USE_QUEUED_RWLOCKS select ARCH_USE_QUEUED_SPINLOCKS -- 2.35.3
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