powerpc: POWER7 optimised memcpy using VMX and enhanced prefetch
Implement a POWER7 optimised memcpy using VMX and enhanced prefetch
instructions.
This is a copy of the POWER7 optimised copy_to_user/copy_from_user
loop. Detailed implementation and performance details can be found in
commit a66086b8197d (powerpc: POWER7 optimised
copy_to_user/copy_from_user using VMX).
I noticed memcpy issues when profiling a RAID6 workload:
.memcpy
.async_memcpy
.async_copy_data
.__raid_run_ops
.handle_stripe
.raid5d
.md_thread
I created a simplified testcase by building a RAID6 array with 4 1GB
ramdisks (booting with brd.rd_size=1048576):
# mdadm -CR -e 1.2 /dev/md0 --level=6 -n4 /dev/ram[0-3]
I then timed how long it took to write to the entire array:
# dd if=/dev/zero of=/dev/md0 bs=1M
Before: 892 MB/s
After: 999 MB/s
A 12% improvement.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/lib/memcpy_64.S b/arch/powerpc/lib/memcpy_64.S
index 82fea39..d2bbbc8 100644
--- a/arch/powerpc/lib/memcpy_64.S
+++ b/arch/powerpc/lib/memcpy_64.S
@@ -11,7 +11,11 @@
.align 7
_GLOBAL(memcpy)
+BEGIN_FTR_SECTION
std r3,48(r1) /* save destination pointer for return value */
+FTR_SECTION_ELSE
+ b memcpy_power7
+ALT_FTR_SECTION_END_IFCLR(CPU_FTR_VMX_COPY)
PPC_MTOCRF(0x01,r5)
cmpldi cr1,r5,16
neg r6,r3 # LS 3 bits = # bytes to 8-byte dest bdry