A number of our chips like loads and stores to be paired. A small kernel
module testcase shows the improvement of pairing loads and stores in
copy_4k_page:
POWER6: +9%
POWER7: +1.5%
#include <linux/module.h>
#include <linux/mm.h>
#define ITERATIONS 10000000
static int __init copypage_init(void)
{
struct timespec before, after;
unsigned long i;
struct page *destpage, *srcpage;
char *dest, *src;
destpage = alloc_page(GFP_KERNEL);
srcpage = alloc_page(GFP_KERNEL);
dest = page_address(destpage);
src = page_address(srcpage);
getnstimeofday(&before);
for (i = 0; i < ITERATIONS; i++)
copy_4K_page(dest, src);
getnstimeofday(&after);
free_page((unsigned long)dest);
free_page((unsigned long)src);
printk(KERN_DEBUG "copy_4K_page loop took %lu ns\n",
(after.tv_sec - before.tv_sec) * NSEC_PER_SEC +
(after.tv_nsec - before.tv_nsec));
return 0;
}
static void __exit copypage_exit(void)
{
}
module_init(copypage_init)
module_exit(copypage_exit)
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Anton Blanchard");
Signed-off-by: Anton Blanchard <an...@samba.org>
---
diff --git a/arch/powerpc/lib/copypage_64.S b/arch/powerpc/lib/copypage_64.S
index 75f3267..22b6c7b 100644
--- a/arch/powerpc/lib/copypage_64.S
+++ b/arch/powerpc/lib/copypage_64.S
@@ -43,62 +43,62 @@ END_FTR_SECTION_IFSET(CPU_FTR_CP_USE_DCBTZ)
ld r7,16(r4)
ldu r8,24(r4)
1: std r5,8(r3)
- ld r9,8(r4)
std r6,16(r3)
+ ld r9,8(r4)
ld r10,16(r4)
std r7,24(r3)
- ld r11,24(r4)
std r8,32(r3)
+ ld r11,24(r4)
ld r12,32(r4)
std r9,40(r3)
- ld r5,40(r4)
std r10,48(r3)
+ ld r5,40(r4)
ld r6,48(r4)
std r11,56(r3)
- ld r7,56(r4)
std r12,64(r3)
+ ld r7,56(r4)
ld r8,64(r4)
std r5,72(r3)
- ld r9,72(r4)
std r6,80(r3)
+ ld r9,72(r4)
ld r10,80(r4)
std r7,88(r3)
- ld r11,88(r4)
std r8,96(r3)
+ ld r11,88(r4)
ld r12,96(r4)
std r9,104(r3)
- ld r5,104(r4)
std r10,112(r3)
+ ld r5,104(r4)
ld r6,112(r4)
std r11,120(r3)
- ld r7,120(r4)
stdu r12,128(r3)
+ ld r7,120(r4)
ldu r8,128(r4)
bdnz 1b
std r5,8(r3)
- ld r9,8(r4)
std r6,16(r3)
+ ld r9,8(r4)
ld r10,16(r4)
std r7,24(r3)
- ld r11,24(r4)
std r8,32(r3)
+ ld r11,24(r4)
ld r12,32(r4)
std r9,40(r3)
- ld r5,40(r4)
std r10,48(r3)
+ ld r5,40(r4)
ld r6,48(r4)
std r11,56(r3)
- ld r7,56(r4)
std r12,64(r3)
+ ld r7,56(r4)
ld r8,64(r4)
std r5,72(r3)
- ld r9,72(r4)
std r6,80(r3)
+ ld r9,72(r4)
ld r10,80(r4)
std r7,88(r3)
- ld r11,88(r4)
std r8,96(r3)
+ ld r11,88(r4)
ld r12,96(r4)
std r9,104(r3)
std r10,112(r3)
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