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x86: atomic64 assembly improvements

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In the "xchg" implementation, %ebx and %ecx don't need to be copied
into %eax and %edx respectively (this is only necessary when desiring
to only read the stored value).

In the "add_unless" implementation, swapping the use of %ecx and %esi
for passing arguments allows %esi to become an input only (i.e.
permitting the register to be re-used to address the same object
without reload).

In "{add,sub}_return", doing the initial read64 through the passed in
%ecx decreases a register dependency.

In "inc_not_zero", a branch can be eliminated by or-ing together the
two halves of the current (64-bit) value, and code size can be further
reduced by adjusting the arithmetic slightly.

v2: Undo the folding of "xchg" and "set".

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Link: http://lkml.kernel.org/r/4F19A2BC020000780006E0DC@nat28.tlf.novell.com
Cc: Luca Barbieri <luca@luca-barbieri.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Jan Beulich 2012-01-20 16:22:04 +00:00 committed by H. Peter Anvin
parent 819165fb34
commit cb8095bba6
3 changed files with 16 additions and 24 deletions
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5
arch/x86/include/asm/atomic64_32.h
View file

@ -288,9 +288,8 @@ static inline int atomic64_add_unless(atomic64_t *v, long long a, long long u)
unsigned low = (unsigned)u;
unsigned high = (unsigned)(u >> 32);
alternative_atomic64(add_unless,
ASM_OUTPUT2("+A" (a), "+c" (v),
"+S" (low), "+D" (high)),
ASM_NO_INPUT_CLOBBER("memory"));
ASM_OUTPUT2("+A" (a), "+c" (low), "+D" (high)),
"S" (v) : "memory");
return (int)a;
}

6
arch/x86/lib/atomic64_386_32.S
View file

@ -137,13 +137,13 @@ BEGIN(dec_return)
RET_ENDP
#undef v
#define v %ecx
#define v %esi
BEGIN(add_unless)
addl %eax, %esi
addl %eax, %ecx
adcl %edx, %edi
addl (v), %eax
adcl 4(v), %edx
cmpl %eax, %esi
cmpl %eax, %ecx
je 3f
1:
movl %eax, (v)

29
arch/x86/lib/atomic64_cx8_32.S
View file

@ -55,8 +55,6 @@ ENDPROC(atomic64_set_cx8)
ENTRY(atomic64_xchg_cx8)
CFI_STARTPROC
movl %ebx, %eax
movl %ecx, %edx
1:
LOCK_PREFIX
cmpxchg8b (%esi)
@ -78,7 +76,7 @@ ENTRY(atomic64_\func\()_return_cx8)
movl %edx, %edi
movl %ecx, %ebp
read64 %ebp
read64 %ecx
1:
movl %eax, %ebx
movl %edx, %ecx
@ -159,23 +157,22 @@ ENTRY(atomic64_add_unless_cx8)
SAVE ebx
/* these just push these two parameters on the stack */
SAVE edi
SAVE esi
SAVE ecx
movl %ecx, %ebp
movl %eax, %esi
movl %eax, %ebp
movl %edx, %edi
read64 %ebp
read64 %esi
1:
cmpl %eax, 0(%esp)
je 4f
2:
movl %eax, %ebx
movl %edx, %ecx
addl %esi, %ebx
addl %ebp, %ebx
adcl %edi, %ecx
LOCK_PREFIX
cmpxchg8b (%ebp)
cmpxchg8b (%esi)
jne 1b
movl $1, %eax
@ -199,13 +196,13 @@ ENTRY(atomic64_inc_not_zero_cx8)
read64 %esi
1:
testl %eax, %eax
je 4f
2:
movl %eax, %ecx
orl %edx, %ecx
jz 3f
movl %eax, %ebx
movl %edx, %ecx
xorl %ecx, %ecx
addl $1, %ebx
adcl $0, %ecx
adcl %edx, %ecx
LOCK_PREFIX
cmpxchg8b (%esi)
jne 1b
@ -214,9 +211,5 @@ ENTRY(atomic64_inc_not_zero_cx8)
3:
RESTORE ebx
ret
4:
testl %edx, %edx
jne 2b
jmp 3b
CFI_ENDPROC
ENDPROC(atomic64_inc_not_zero_cx8)