From 5284e1b4bc8ae6fcc1c92c63cf6c876a53292f82 Mon Sep 17 00:00:00 2001 From: Steve Capper Date: Fri, 24 Oct 2014 13:22:20 +0100 Subject: [PATCH] arm64: xchg: Implement cmpxchg_double The arm64 architecture has the ability to exclusively load and store a pair of registers from an address (ldxp/stxp). Also the SLUB can take advantage of a cmpxchg_double implementation to avoid taking some locks. This patch provides an implementation of cmpxchg_double for 64-bit pairs, and activates the logic required for the SLUB to use these functions (HAVE_ALIGNED_STRUCT_PAGE and HAVE_CMPXCHG_DOUBLE). Also definitions of this_cpu_cmpxchg_8 and this_cpu_cmpxchg_double_8 are wired up to cmpxchg_local and cmpxchg_double_local (rather than the stock implementations that perform non-atomic operations with interrupts disabled) as they are used by the SLUB. On a Juno platform running on only the A57s I get quite a noticeable performance improvement with 5 runs of hackbench on v3.17: Baseline | With Patch -----------------+----------- Mean 119.2312 | 106.1782 StdDev 0.4919 | 0.4494 (times taken to complete `./hackbench 100 process 1000', in seconds) Signed-off-by: Steve Capper Signed-off-by: Will Deacon --- arch/arm64/Kconfig | 2 + arch/arm64/include/asm/cmpxchg.h | 71 ++++++++++++++++++++++++++++++++ 2 files changed, 73 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 2c3c2ca6f8bc..1e0e4671dd25 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -34,6 +34,7 @@ config ARM64 select GENERIC_TIME_VSYSCALL select HANDLE_DOMAIN_IRQ select HARDIRQS_SW_RESEND + select HAVE_ALIGNED_STRUCT_PAGE if SLUB select HAVE_ARCH_AUDITSYSCALL select HAVE_ARCH_JUMP_LABEL select HAVE_ARCH_KGDB @@ -41,6 +42,7 @@ config ARM64 select HAVE_BPF_JIT select HAVE_C_RECORDMCOUNT select HAVE_CC_STACKPROTECTOR + select HAVE_CMPXCHG_DOUBLE select HAVE_DEBUG_BUGVERBOSE select HAVE_DEBUG_KMEMLEAK select HAVE_DMA_API_DEBUG diff --git a/arch/arm64/include/asm/cmpxchg.h b/arch/arm64/include/asm/cmpxchg.h index ddb9d7830558..89e397befad5 100644 --- a/arch/arm64/include/asm/cmpxchg.h +++ b/arch/arm64/include/asm/cmpxchg.h @@ -19,6 +19,7 @@ #define __ASM_CMPXCHG_H #include +#include #include @@ -152,6 +153,51 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old, return oldval; } +#define system_has_cmpxchg_double() 1 + +static inline int __cmpxchg_double(volatile void *ptr1, volatile void *ptr2, + unsigned long old1, unsigned long old2, + unsigned long new1, unsigned long new2, int size) +{ + unsigned long loop, lost; + + switch (size) { + case 8: + VM_BUG_ON((unsigned long *)ptr2 - (unsigned long *)ptr1 != 1); + do { + asm volatile("// __cmpxchg_double8\n" + " ldxp %0, %1, %2\n" + " eor %0, %0, %3\n" + " eor %1, %1, %4\n" + " orr %1, %0, %1\n" + " mov %w0, #0\n" + " cbnz %1, 1f\n" + " stxp %w0, %5, %6, %2\n" + "1:\n" + : "=&r"(loop), "=&r"(lost), "+Q" (*(u64 *)ptr1) + : "r" (old1), "r"(old2), "r"(new1), "r"(new2)); + } while (loop); + break; + default: + BUILD_BUG(); + } + + return !lost; +} + +static inline int __cmpxchg_double_mb(volatile void *ptr1, volatile void *ptr2, + unsigned long old1, unsigned long old2, + unsigned long new1, unsigned long new2, int size) +{ + int ret; + + smp_mb(); + ret = __cmpxchg_double(ptr1, ptr2, old1, old2, new1, new2, size); + smp_mb(); + + return ret; +} + static inline unsigned long __cmpxchg_mb(volatile void *ptr, unsigned long old, unsigned long new, int size) { @@ -182,6 +228,31 @@ static inline unsigned long __cmpxchg_mb(volatile void *ptr, unsigned long old, __ret; \ }) +#define cmpxchg_double(ptr1, ptr2, o1, o2, n1, n2) \ +({\ + int __ret;\ + __ret = __cmpxchg_double_mb((ptr1), (ptr2), (unsigned long)(o1), \ + (unsigned long)(o2), (unsigned long)(n1), \ + (unsigned long)(n2), sizeof(*(ptr1)));\ + __ret; \ +}) + +#define cmpxchg_double_local(ptr1, ptr2, o1, o2, n1, n2) \ +({\ + int __ret;\ + __ret = __cmpxchg_double((ptr1), (ptr2), (unsigned long)(o1), \ + (unsigned long)(o2), (unsigned long)(n1), \ + (unsigned long)(n2), sizeof(*(ptr1)));\ + __ret; \ +}) + +#define this_cpu_cmpxchg_8(ptr, o, n) \ + cmpxchg_local(raw_cpu_ptr(&(ptr)), o, n) + +#define this_cpu_cmpxchg_double_8(ptr1, ptr2, o1, o2, n1, n2) \ + cmpxchg_double_local(raw_cpu_ptr(&(ptr1)), raw_cpu_ptr(&(ptr2)), \ + o1, o2, n1, n2) + #define cmpxchg64(ptr,o,n) cmpxchg((ptr),(o),(n)) #define cmpxchg64_local(ptr,o,n) cmpxchg_local((ptr),(o),(n)) -- 2.20.1