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 <steve.capper@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
diff --git a/arch/arm64/include/asm/cmpxchg.h b/arch/arm64/include/asm/cmpxchg.h
index ddb9d78..89e397b 100644
--- a/arch/arm64/include/asm/cmpxchg.h
+++ b/arch/arm64/include/asm/cmpxchg.h
@@ -19,6 +19,7 @@
#define __ASM_CMPXCHG_H
#include <linux/bug.h>
+#include <linux/mmdebug.h>
#include <asm/barrier.h>
@@ -152,6 +153,51 @@
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 @@
__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))