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arm64: atomics: prefetch the destination word for write prior to stxr 

The cost of changing a cacheline from shared to exclusive state can be
significant, especially when this is triggered by an exclusive store,
since it may result in having to retry the transaction.

This patch makes use of prfm to prefetch cachelines for write prior to
ldxr/stxr loops when using the ll/sc atomic routines.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Will Deacon 2015-05-29 13:31:10 +01:00
parent a82e62382f
commit 0ea366f5e1
4 changed files with 21 additions and 0 deletions
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9
arch/arm64/include/asm/atomic_ll_sc.h
View File

@ -45,6 +45,7 @@ __LL_SC_PREFIX(atomic_##op(int i, atomic_t *v)) \
int result; \
\
asm volatile("// atomic_" #op "\n" \
" prfm pstl1strm, %2\n" \
"1: ldxr %w0, %2\n" \
" " #asm_op " %w0, %w0, %w3\n" \
" stxr %w1, %w0, %2\n" \
@ -62,6 +63,7 @@ __LL_SC_PREFIX(atomic_##op##_return(int i, atomic_t *v)) \
int result; \
\
asm volatile("// atomic_" #op "_return\n" \
" prfm pstl1strm, %2\n" \
"1: ldxr %w0, %2\n" \
" " #asm_op " %w0, %w0, %w3\n" \
" stlxr %w1, %w0, %2\n" \
@ -98,6 +100,7 @@ __LL_SC_PREFIX(atomic_cmpxchg(atomic_t *ptr, int old, int new))
int oldval;
asm volatile("// atomic_cmpxchg\n"
" prfm pstl1strm, %2\n"
"1: ldxr %w1, %2\n"
" eor %w0, %w1, %w3\n"
" cbnz %w0, 2f\n"
@ -121,6 +124,7 @@ __LL_SC_PREFIX(atomic64_##op(long i, atomic64_t *v)) \
unsigned long tmp; \
\
asm volatile("// atomic64_" #op "\n" \
" prfm pstl1strm, %2\n" \
"1: ldxr %0, %2\n" \
" " #asm_op " %0, %0, %3\n" \
" stxr %w1, %0, %2\n" \
@ -138,6 +142,7 @@ __LL_SC_PREFIX(atomic64_##op##_return(long i, atomic64_t *v)) \
unsigned long tmp; \
\
asm volatile("// atomic64_" #op "_return\n" \
" prfm pstl1strm, %2\n" \
"1: ldxr %0, %2\n" \
" " #asm_op " %0, %0, %3\n" \
" stlxr %w1, %0, %2\n" \
@ -174,6 +179,7 @@ __LL_SC_PREFIX(atomic64_cmpxchg(atomic64_t *ptr, long old, long new))
unsigned long res;
asm volatile("// atomic64_cmpxchg\n"
" prfm pstl1strm, %2\n"
"1: ldxr %1, %2\n"
" eor %0, %1, %3\n"
" cbnz %w0, 2f\n"
@ -196,6 +202,7 @@ __LL_SC_PREFIX(atomic64_dec_if_positive(atomic64_t *v))
unsigned long tmp;
asm volatile("// atomic64_dec_if_positive\n"
" prfm pstl1strm, %2\n"
"1: ldxr %0, %2\n"
" subs %0, %0, #1\n"
" b.mi 2f\n"
@ -220,6 +227,7 @@ __LL_SC_PREFIX(__cmpxchg_case_##name(volatile void *ptr, \
unsigned long tmp, oldval; \
\
asm volatile( \
" prfm pstl1strm, %2\n" \
"1: ldxr" #sz "\t%" #w "[oldval], %[v]\n" \
" eor %" #w "[tmp], %" #w "[oldval], %" #w "[old]\n" \
" cbnz %" #w "[tmp], 2f\n" \
@ -259,6 +267,7 @@ __LL_SC_PREFIX(__cmpxchg_double##name(unsigned long old1, \
unsigned long tmp, ret; \
\
asm volatile("// __cmpxchg_double" #name "\n" \
" prfm pstl1strm, %2\n" \
"1: ldxp %0, %1, %2\n" \
" eor %0, %0, %3\n" \
" eor %1, %1, %4\n" \

8
arch/arm64/include/asm/cmpxchg.h
View File

@ -33,12 +33,14 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
case 1:
asm volatile(ARM64_LSE_ATOMIC_INSN(
/* LL/SC */
" prfm pstl1strm, %2\n"
"1: ldxrb %w0, %2\n"
" stlxrb %w1, %w3, %2\n"
" cbnz %w1, 1b\n"
" dmb ish",
/* LSE atomics */
" nop\n"
" nop\n"
" swpalb %w3, %w0, %2\n"
" nop\n"
" nop")
@ -49,12 +51,14 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
case 2:
asm volatile(ARM64_LSE_ATOMIC_INSN(
/* LL/SC */
" prfm pstl1strm, %2\n"
"1: ldxrh %w0, %2\n"
" stlxrh %w1, %w3, %2\n"
" cbnz %w1, 1b\n"
" dmb ish",
/* LSE atomics */
" nop\n"
" nop\n"
" swpalh %w3, %w0, %2\n"
" nop\n"
" nop")
@ -65,12 +69,14 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
case 4:
asm volatile(ARM64_LSE_ATOMIC_INSN(
/* LL/SC */
" prfm pstl1strm, %2\n"
"1: ldxr %w0, %2\n"
" stlxr %w1, %w3, %2\n"
" cbnz %w1, 1b\n"
" dmb ish",
/* LSE atomics */
" nop\n"
" nop\n"
" swpal %w3, %w0, %2\n"
" nop\n"
" nop")
@ -81,12 +87,14 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
case 8:
asm volatile(ARM64_LSE_ATOMIC_INSN(
/* LL/SC */
" prfm pstl1strm, %2\n"
"1: ldxr %0, %2\n"
" stlxr %w1, %3, %2\n"
" cbnz %w1, 1b\n"
" dmb ish",
/* LSE atomics */
" nop\n"
" nop\n"
" swpal %3, %0, %2\n"
" nop\n"
" nop")

2
arch/arm64/include/asm/futex.h
View File

@ -30,6 +30,7 @@
asm volatile( \
ALTERNATIVE("nop", SET_PSTATE_PAN(0), ARM64_HAS_PAN, \
CONFIG_ARM64_PAN) \
" prfm pstl1strm, %2\n" \
"1: ldxr %w1, %2\n" \
insn "\n" \
"2: stlxr %w3, %w0, %2\n" \
@ -120,6 +121,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
return -EFAULT;
asm volatile("// futex_atomic_cmpxchg_inatomic\n"
" prfm pstl1strm, %2\n"
"1: ldxr %w1, %2\n"
" sub %w3, %w1, %w4\n"
" cbnz %w3, 3f\n"

2
arch/arm64/lib/bitops.S
View File

@ -31,6 +31,7 @@ ENTRY( \name )
eor w0, w0, w3 // Clear low bits
mov x2, #1
add x1, x1, x0, lsr #3 // Get word offset
alt_lse " prfm pstl1strm, [x1]", "nop"
lsl x3, x2, x3 // Create mask
alt_lse "1: ldxr x2, [x1]", "\lse x3, [x1]"
@ -48,6 +49,7 @@ ENTRY( \name )
eor w0, w0, w3 // Clear low bits
mov x2, #1
add x1, x1, x0, lsr #3 // Get word offset
alt_lse " prfm pstl1strm, [x1]", "nop"
lsl x4, x2, x3 // Create mask
alt_lse "1: ldxr x2, [x1]", "\lse x4, x2, [x1]"