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Commit cb8095bb authored by Jan Beulich's avatar Jan Beulich Committed by H. Peter Anvin
Browse files

x86: atomic64 assembly improvements 



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: default avatarJan 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: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent 819165fb

arch/x86/include/asm/atomic64_32.h

+2 −3
Original line number Diff line number Diff line
@@ -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;

}

arch/x86/lib/atomic64_386_32.S

+3 −3
Original line number Diff line number Diff line
@@ -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)

arch/x86/lib/atomic64_cx8_32.S

+11 −18
Original line number Diff line number Diff line
@@ -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)