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| author | Peter Zijlstra <peterz@infradead.org> | 2013-09-11 15:19:24 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2013-09-25 13:53:08 +0200 |
| commit | 0c44c2d0f459cd7e275242b72f500137c4fa834d (patch) | |
| tree | fdd16d5585a986cf8cbed140f533d08d152bbc4f /arch/x86/include/asm/rmwcc.h | |
| parent | sched: Micro-optimize by dropping unnecessary task_rq() calls (diff) | |
| download | linux-0c44c2d0f459cd7e275242b72f500137c4fa834d.tar.xz linux-0c44c2d0f459cd7e275242b72f500137c4fa834d.zip | |
x86: Use asm goto to implement better modify_and_test() functions
Linus suggested using asm goto to get rid of the typical SETcc + TEST
instruction pair -- which also clobbers an extra register -- for our
typical modify_and_test() functions.
Because asm goto doesn't allow output fields it has to include an
unconditinal memory clobber when it changes a memory variable to force
a reload.
Luckily all atomic ops already imply a compiler barrier to go along
with their memory barrier semantics.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-0mtn9siwbeo1d33bap1422se@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/include/asm/rmwcc.h')
| -rw-r--r-- | arch/x86/include/asm/rmwcc.h | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/arch/x86/include/asm/rmwcc.h b/arch/x86/include/asm/rmwcc.h new file mode 100644 index 000000000000..735f1849795f --- /dev/null +++ b/arch/x86/include/asm/rmwcc.h @@ -0,0 +1,41 @@ +#ifndef _ASM_X86_RMWcc +#define _ASM_X86_RMWcc + +#ifdef CC_HAVE_ASM_GOTO + +#define __GEN_RMWcc(fullop, var, cc, ...) \ +do { \ + asm volatile goto (fullop "; j" cc " %l[cc_label]" \ + : : "m" (var), ## __VA_ARGS__ \ + : "memory" : cc_label); \ + return 0; \ +cc_label: \ + return 1; \ +} while (0) + +#define GEN_UNARY_RMWcc(op, var, arg0, cc) \ + __GEN_RMWcc(op " " arg0, var, cc) + +#define GEN_BINARY_RMWcc(op, var, val, arg0, cc) \ + __GEN_RMWcc(op " %1, " arg0, var, cc, "er" (val)) + +#else /* !CC_HAVE_ASM_GOTO */ + +#define __GEN_RMWcc(fullop, var, cc, ...) \ +do { \ + char c; \ + asm volatile (fullop "; set" cc " %1" \ + : "+m" (var), "=qm" (c) \ + : __VA_ARGS__ : "memory"); \ + return c != 0; \ +} while (0) + +#define GEN_UNARY_RMWcc(op, var, arg0, cc) \ + __GEN_RMWcc(op " " arg0, var, cc) + +#define GEN_BINARY_RMWcc(op, var, val, arg0, cc) \ + __GEN_RMWcc(op " %2, " arg0, var, cc, "er" (val)) + +#endif /* CC_HAVE_ASM_GOTO */ + +#endif /* _ASM_X86_RMWcc */ |