Commit-ID: 1966c5e5bd9802cf62d3744ef4d2d6d32e22604d
Gitweb: https://git.kernel.org/tip/1966c5e5bd9802cf62d3744ef4d2d6d32e22604d
Author: Uros Bizjak <ubizjak@xxxxxxxxx>
AuthorDate: Tue, 5 Jun 2018 18:39:09 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 21 Jun 2018 15:21:47 +0200
x86/asm: Use CC_SET/CC_OUT in percpu_cmpxchg8b_double() to micro-optimize code generation
Use CC_SET(z)/CC_OUT(z) instead of explicit SETZ instruction.
Using these two defines, the compiler that supports generation of
condition code outputs from inline assembly flags generates e.g.:
cmpxchg8b %fs:(%esi)
jne 172255 <__kmalloc+0x65>
instead of:
cmpxchg8b %fs:(%esi)
sete %al
test %al,%al
je 172255 <__kmalloc+0x65>
Note that older compilers now generate:
cmpxchg8b %fs:(%esi)
sete %cl
test %cl,%cl
je 173a85 <__kmalloc+0x65>
since we have to mark that cmpxchg8b instruction outputs to %eax
register and this way clobbers the value in the register.
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/20180605163910.13015-1-ubizjak@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/include/asm/percpu.h | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index a06b07399d17..e9202a0de8f0 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -450,9 +450,10 @@ do { \
bool __ret; \
typeof(pcp1) __o1 = (o1), __n1 = (n1); \
typeof(pcp2) __o2 = (o2), __n2 = (n2); \
- asm volatile("cmpxchg8b "__percpu_arg(1)"\n\tsetz %0\n\t" \
- : "=a" (__ret), "+m" (pcp1), "+m" (pcp2), "+d" (__o2) \
- : "b" (__n1), "c" (__n2), "a" (__o1)); \
+ asm volatile("cmpxchg8b "__percpu_arg(1) \
+ CC_SET(z) \
+ : CC_OUT(z) (__ret), "+m" (pcp1), "+m" (pcp2), "+a" (__o1), "+d" (__o2) \
+ : "b" (__n1), "c" (__n2)); \
__ret; \
})
--
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