From: will.deacon@arm.com (Will Deacon) Date: Thu, 25 Jul 2013 16:55:39 +0100 Subject: [PATCH v2 5/6] ARM: atomics: prefetch the destination word for write prior to strex In-Reply-To: <1374767740-2068-1-git-send-email-will.deacon@arm.com> References: <1374767740-2068-1-git-send-email-will.deacon@arm.com> Message-ID: <1374767740-2068-6-git-send-email-will.deacon@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 prefixes our atomic access implementations with pldw instructions (on CPUs which support them) to try and grab the line in exclusive state from the start. Only the barrier-less functions are updated, since memory barriers can limit the usefulness of prefetching data. Signed-off-by: Will Deacon --- arch/arm/include/asm/atomic.h | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/arm/include/asm/atomic.h b/arch/arm/include/asm/atomic.h index da1c77d..55ffc3b 100644 --- a/arch/arm/include/asm/atomic.h +++ b/arch/arm/include/asm/atomic.h @@ -12,6 +12,7 @@ #define __ASM_ARM_ATOMIC_H #include +#include #include #include #include @@ -41,6 +42,7 @@ static inline void atomic_add(int i, atomic_t *v) unsigned long tmp; int result; + prefetchw(&v->counter); __asm__ __volatile__("@ atomic_add\n" "1: ldrex %0, [%3]\n" " add %0, %0, %4\n" @@ -79,6 +81,7 @@ static inline void atomic_sub(int i, atomic_t *v) unsigned long tmp; int result; + prefetchw(&v->counter); __asm__ __volatile__("@ atomic_sub\n" "1: ldrex %0, [%3]\n" " sub %0, %0, %4\n" @@ -138,6 +141,7 @@ static inline void atomic_clear_mask(unsigned long mask, unsigned long *addr) { unsigned long tmp, tmp2; + prefetchw(addr); __asm__ __volatile__("@ atomic_clear_mask\n" "1: ldrex %0, [%3]\n" " bic %0, %0, %4\n" @@ -283,6 +287,7 @@ static inline void atomic64_set(atomic64_t *v, u64 i) { u64 tmp; + prefetchw(&v->counter); __asm__ __volatile__("@ atomic64_set\n" "1: ldrexd %0, %H0, [%2]\n" " strexd %0, %3, %H3, [%2]\n" @@ -299,6 +304,7 @@ static inline void atomic64_add(u64 i, atomic64_t *v) u64 result; unsigned long tmp; + prefetchw(&v->counter); __asm__ __volatile__("@ atomic64_add\n" "1: ldrexd %0, %H0, [%3]\n" " adds %0, %0, %4\n" @@ -339,6 +345,7 @@ static inline void atomic64_sub(u64 i, atomic64_t *v) u64 result; unsigned long tmp; + prefetchw(&v->counter); __asm__ __volatile__("@ atomic64_sub\n" "1: ldrexd %0, %H0, [%3]\n" " subs %0, %0, %4\n" -- 1.8.2.2