From: Wedson Almeida Filho Date: Fri, 28 Jun 2013 11:50:45 +0000 (-0700) Subject: x86: Use asm-goto to implement mutex fast path on x86-64 X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=00e55a790706223c903ce6a450c18596a7bc9be0;p=deliverable%2Flinux.git x86: Use asm-goto to implement mutex fast path on x86-64 The new implementation allows the compiler to better optimize the code; the original implementation is still used when the kernel is compiled with older versions of gcc that don't support asm-goto. Compiling with gcc 4.7.3, the original mutex_lock() is 60 bytes with the fast path taking 16 instructions; the new mutex_lock() is 42 bytes, with the fast path taking 12 instructions. The original mutex_unlock() is 24 bytes with the fast path taking 7 instructions; the new mutex_unlock() is 25 bytes (because the compiler used a 2-byte ret) with the fast path taking 4 instructions. The two versions of the functions are included below for reference. Old: ffffffff817742a0 : ffffffff817742a0: 55 push %rbp ffffffff817742a1: 48 89 e5 mov %rsp,%rbp ffffffff817742a4: 48 83 ec 10 sub $0x10,%rsp ffffffff817742a8: 48 89 5d f0 mov %rbx,-0x10(%rbp) ffffffff817742ac: 48 89 fb mov %rdi,%rbx ffffffff817742af: 4c 89 65 f8 mov %r12,-0x8(%rbp) ffffffff817742b3: e8 28 15 00 00 callq ffffffff817757e0 <_cond_resched> ffffffff817742b8: 48 89 df mov %rbx,%rdi ffffffff817742bb: f0 ff 0f lock decl (%rdi) ffffffff817742be: 79 05 jns ffffffff817742c5 ffffffff817742c0: e8 cb 04 00 00 callq ffffffff81774790 <__mutex_lock_slowpath> ffffffff817742c5: 65 48 8b 04 25 c0 b7 mov %gs:0xb7c0,%rax ffffffff817742cc: 00 00 ffffffff817742ce: 4c 8b 65 f8 mov -0x8(%rbp),%r12 ffffffff817742d2: 48 89 43 18 mov %rax,0x18(%rbx) ffffffff817742d6: 48 8b 5d f0 mov -0x10(%rbp),%rbx ffffffff817742da: c9 leaveq ffffffff817742db: c3 retq ffffffff81774250 : ffffffff81774250: 55 push %rbp ffffffff81774251: 48 c7 47 18 00 00 00 movq $0x0,0x18(%rdi) ffffffff81774258: 00 ffffffff81774259: 48 89 e5 mov %rsp,%rbp ffffffff8177425c: f0 ff 07 lock incl (%rdi) ffffffff8177425f: 7f 05 jg ffffffff81774266 ffffffff81774261: e8 ea 04 00 00 callq ffffffff81774750 <__mutex_unlock_slowpath> ffffffff81774266: 5d pop %rbp ffffffff81774267: c3 retq New: ffffffff81774920 : ffffffff81774920: 55 push %rbp ffffffff81774921: 48 89 e5 mov %rsp,%rbp ffffffff81774924: 53 push %rbx ffffffff81774925: 48 89 fb mov %rdi,%rbx ffffffff81774928: e8 a3 0e 00 00 callq ffffffff817757d0 <_cond_resched> ffffffff8177492d: f0 ff 0b lock decl (%rbx) ffffffff81774930: 79 08 jns ffffffff8177493a ffffffff81774932: 48 89 df mov %rbx,%rdi ffffffff81774935: e8 16 fe ff ff callq ffffffff81774750 <__mutex_lock_slowpath> ffffffff8177493a: 65 48 8b 04 25 c0 b7 mov %gs:0xb7c0,%rax ffffffff81774941: 00 00 ffffffff81774943: 48 89 43 18 mov %rax,0x18(%rbx) ffffffff81774947: 5b pop %rbx ffffffff81774948: 5d pop %rbp ffffffff81774949: c3 retq ffffffff81774730 : ffffffff81774730: 48 c7 47 18 00 00 00 movq $0x0,0x18(%rdi) ffffffff81774737: 00 ffffffff81774738: f0 ff 07 lock incl (%rdi) ffffffff8177473b: 7f 0a jg ffffffff81774747 ffffffff8177473d: 55 push %rbp ffffffff8177473e: 48 89 e5 mov %rsp,%rbp ffffffff81774741: e8 aa ff ff ff callq ffffffff817746f0 <__mutex_unlock_slowpath> ffffffff81774746: 5d pop %rbp ffffffff81774747: f3 c3 repz retq Signed-off-by: Wedson Almeida Filho Link: http://lkml.kernel.org/r/1372420245-60021-1-git-send-email-wedsonaf@gmail.com Signed-off-by: H. Peter Anvin --- diff --git a/arch/x86/include/asm/mutex_64.h b/arch/x86/include/asm/mutex_64.h index 68a87b0f8e29..c030bee7690a 100644 --- a/arch/x86/include/asm/mutex_64.h +++ b/arch/x86/include/asm/mutex_64.h @@ -16,6 +16,20 @@ * * Atomically decrements @v and calls if the result is negative. */ +#ifdef CC_HAVE_ASM_GOTO +static inline void __mutex_fastpath_lock(atomic_t *v, + void (*fail_fn)(atomic_t *)) +{ + asm volatile goto(LOCK_PREFIX " decl %0\n" + " jns %l[exit]\n" + : : "m" (v->counter) + : "memory", "cc" + : exit); + fail_fn(v); +exit: + return; +} +#else #define __mutex_fastpath_lock(v, fail_fn) \ do { \ unsigned long dummy; \ @@ -32,6 +46,7 @@ do { \ : "rax", "rsi", "rdx", "rcx", \ "r8", "r9", "r10", "r11", "memory"); \ } while (0) +#endif /** * __mutex_fastpath_lock_retval - try to take the lock by moving the count @@ -59,6 +74,20 @@ static inline int __mutex_fastpath_lock_retval(atomic_t *count, * * Atomically increments @v and calls if the result is nonpositive. */ +#ifdef CC_HAVE_ASM_GOTO +static inline void __mutex_fastpath_unlock(atomic_t *v, + void (*fail_fn)(atomic_t *)) +{ + asm volatile goto(LOCK_PREFIX " incl %0\n" + " jg %l[exit]\n" + : : "m" (v->counter) + : "memory", "cc" + : exit); + fail_fn(v); +exit: + return; +} +#else #define __mutex_fastpath_unlock(v, fail_fn) \ do { \ unsigned long dummy; \ @@ -75,6 +104,7 @@ do { \ : "rax", "rsi", "rdx", "rcx", \ "r8", "r9", "r10", "r11", "memory"); \ } while (0) +#endif #define __mutex_slowpath_needs_to_unlock() 1