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x86: Use asm goto to implement better modify_and_test() functions
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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>
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Peter Zijlstra authored and Ingo Molnar committed Sep 25, 2013
1 parent 4314895 commit 0c44c2d
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Showing 5 changed files with 58 additions and 92 deletions.
29 changes: 5 additions & 24 deletions arch/x86/include/asm/atomic.h
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@
#include <asm/processor.h>
#include <asm/alternative.h>
#include <asm/cmpxchg.h>
#include <asm/rmwcc.h>

/*
* Atomic operations that C can't guarantee us. Useful for
Expand Down Expand Up @@ -76,12 +77,7 @@ static inline void atomic_sub(int i, atomic_t *v)
*/
static inline int atomic_sub_and_test(int i, atomic_t *v)
{
unsigned char c;

asm volatile(LOCK_PREFIX "subl %2,%0; sete %1"
: "+m" (v->counter), "=qm" (c)
: "ir" (i) : "memory");
return c;
GEN_BINARY_RMWcc(LOCK_PREFIX "subl", v->counter, i, "%0", "e");
}

/**
Expand Down Expand Up @@ -118,12 +114,7 @@ static inline void atomic_dec(atomic_t *v)
*/
static inline int atomic_dec_and_test(atomic_t *v)
{
unsigned char c;

asm volatile(LOCK_PREFIX "decl %0; sete %1"
: "+m" (v->counter), "=qm" (c)
: : "memory");
return c != 0;
GEN_UNARY_RMWcc(LOCK_PREFIX "decl", v->counter, "%0", "e");
}

/**
Expand All @@ -136,12 +127,7 @@ static inline int atomic_dec_and_test(atomic_t *v)
*/
static inline int atomic_inc_and_test(atomic_t *v)
{
unsigned char c;

asm volatile(LOCK_PREFIX "incl %0; sete %1"
: "+m" (v->counter), "=qm" (c)
: : "memory");
return c != 0;
GEN_UNARY_RMWcc(LOCK_PREFIX "incl", v->counter, "%0", "e");
}

/**
Expand All @@ -155,12 +141,7 @@ static inline int atomic_inc_and_test(atomic_t *v)
*/
static inline int atomic_add_negative(int i, atomic_t *v)
{
unsigned char c;

asm volatile(LOCK_PREFIX "addl %2,%0; sets %1"
: "+m" (v->counter), "=qm" (c)
: "ir" (i) : "memory");
return c;
GEN_BINARY_RMWcc(LOCK_PREFIX "addl", v->counter, i, "%0", "s");
}

/**
Expand Down
28 changes: 4 additions & 24 deletions arch/x86/include/asm/atomic64_64.h
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Original file line number Diff line number Diff line change
Expand Up @@ -72,12 +72,7 @@ static inline void atomic64_sub(long i, atomic64_t *v)
*/
static inline int atomic64_sub_and_test(long i, atomic64_t *v)
{
unsigned char c;

asm volatile(LOCK_PREFIX "subq %2,%0; sete %1"
: "=m" (v->counter), "=qm" (c)
: "er" (i), "m" (v->counter) : "memory");
return c;
GEN_BINARY_RMWcc(LOCK_PREFIX "subq", v->counter, i, "%0", "e");
}

/**
Expand Down Expand Up @@ -116,12 +111,7 @@ static inline void atomic64_dec(atomic64_t *v)
*/
static inline int atomic64_dec_and_test(atomic64_t *v)
{
unsigned char c;

asm volatile(LOCK_PREFIX "decq %0; sete %1"
: "=m" (v->counter), "=qm" (c)
: "m" (v->counter) : "memory");
return c != 0;
GEN_UNARY_RMWcc(LOCK_PREFIX "decq", v->counter, "%0", "e");
}

/**
Expand All @@ -134,12 +124,7 @@ static inline int atomic64_dec_and_test(atomic64_t *v)
*/
static inline int atomic64_inc_and_test(atomic64_t *v)
{
unsigned char c;

asm volatile(LOCK_PREFIX "incq %0; sete %1"
: "=m" (v->counter), "=qm" (c)
: "m" (v->counter) : "memory");
return c != 0;
GEN_UNARY_RMWcc(LOCK_PREFIX "incq", v->counter, "%0", "e");
}

/**
Expand All @@ -153,12 +138,7 @@ static inline int atomic64_inc_and_test(atomic64_t *v)
*/
static inline int atomic64_add_negative(long i, atomic64_t *v)
{
unsigned char c;

asm volatile(LOCK_PREFIX "addq %2,%0; sets %1"
: "=m" (v->counter), "=qm" (c)
: "er" (i), "m" (v->counter) : "memory");
return c;
GEN_BINARY_RMWcc(LOCK_PREFIX "addq", v->counter, i, "%0", "s");
}

/**
Expand Down
24 changes: 4 additions & 20 deletions arch/x86/include/asm/bitops.h
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@

#include <linux/compiler.h>
#include <asm/alternative.h>
#include <asm/rmwcc.h>

#if BITS_PER_LONG == 32
# define _BITOPS_LONG_SHIFT 5
Expand Down Expand Up @@ -204,12 +205,7 @@ static inline void change_bit(long nr, volatile unsigned long *addr)
*/
static inline int test_and_set_bit(long nr, volatile unsigned long *addr)
{
int oldbit;

asm volatile(LOCK_PREFIX "bts %2,%1\n\t"
"sbb %0,%0" : "=r" (oldbit), ADDR : "Ir" (nr) : "memory");

return oldbit;
GEN_BINARY_RMWcc(LOCK_PREFIX "bts", *addr, nr, "%0", "c");
}

/**
Expand Down Expand Up @@ -255,13 +251,7 @@ static inline int __test_and_set_bit(long nr, volatile unsigned long *addr)
*/
static inline int test_and_clear_bit(long nr, volatile unsigned long *addr)
{
int oldbit;

asm volatile(LOCK_PREFIX "btr %2,%1\n\t"
"sbb %0,%0"
: "=r" (oldbit), ADDR : "Ir" (nr) : "memory");

return oldbit;
GEN_BINARY_RMWcc(LOCK_PREFIX "btr", *addr, nr, "%0", "c");
}

/**
Expand Down Expand Up @@ -314,13 +304,7 @@ static inline int __test_and_change_bit(long nr, volatile unsigned long *addr)
*/
static inline int test_and_change_bit(long nr, volatile unsigned long *addr)
{
int oldbit;

asm volatile(LOCK_PREFIX "btc %2,%1\n\t"
"sbb %0,%0"
: "=r" (oldbit), ADDR : "Ir" (nr) : "memory");

return oldbit;
GEN_BINARY_RMWcc(LOCK_PREFIX "btc", *addr, nr, "%0", "c");
}

static __always_inline int constant_test_bit(long nr, const volatile unsigned long *addr)
Expand Down
28 changes: 4 additions & 24 deletions arch/x86/include/asm/local.h
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Original file line number Diff line number Diff line change
Expand Up @@ -52,12 +52,7 @@ static inline void local_sub(long i, local_t *l)
*/
static inline int local_sub_and_test(long i, local_t *l)
{
unsigned char c;

asm volatile(_ASM_SUB "%2,%0; sete %1"
: "+m" (l->a.counter), "=qm" (c)
: "ir" (i) : "memory");
return c;
GEN_BINARY_RMWcc(_ASM_SUB, l->a.counter, i, "%0", "e");
}

/**
Expand All @@ -70,12 +65,7 @@ static inline int local_sub_and_test(long i, local_t *l)
*/
static inline int local_dec_and_test(local_t *l)
{
unsigned char c;

asm volatile(_ASM_DEC "%0; sete %1"
: "+m" (l->a.counter), "=qm" (c)
: : "memory");
return c != 0;
GEN_UNARY_RMWcc(_ASM_DEC, l->a.counter, "%0", "e");
}

/**
Expand All @@ -88,12 +78,7 @@ static inline int local_dec_and_test(local_t *l)
*/
static inline int local_inc_and_test(local_t *l)
{
unsigned char c;

asm volatile(_ASM_INC "%0; sete %1"
: "+m" (l->a.counter), "=qm" (c)
: : "memory");
return c != 0;
GEN_UNARY_RMWcc(_ASM_INC, l->a.counter, "%0", "e");
}

/**
Expand All @@ -107,12 +92,7 @@ static inline int local_inc_and_test(local_t *l)
*/
static inline int local_add_negative(long i, local_t *l)
{
unsigned char c;

asm volatile(_ASM_ADD "%2,%0; sets %1"
: "+m" (l->a.counter), "=qm" (c)
: "ir" (i) : "memory");
return c;
GEN_BINARY_RMWcc(_ASM_ADD, l->a.counter, i, "%0", "s");
}

/**
Expand Down
41 changes: 41 additions & 0 deletions arch/x86/include/asm/rmwcc.h
View file
Original file line number Diff line number Diff line change
@@ -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 */

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