[PATCH 2/2] powerpc: POWER7 optimised copy_page using VMX and enhanced prefetch
Anton Blanchard
anton at samba.org
Wed May 30 15:33:12 EST 2012
Implement a POWER7 optimised copy_page using VMX and enhanced
prefetch instructions. We use enhanced prefetch hints to prefetch
both the load and store side. We copy a cacheline at a time and
fall back to regular loads and stores if we are unable to use VMX
(eg we are in an interrupt).
The following microbenchmark was used to assess the impact of
the patch:
http://ozlabs.org/~anton/junkcode/page_fault_file.c
We test MAP_PRIVATE page faults across a 1GB file, 100 times:
# time ./page_fault_file -p -l 1G -i 100
Before: 22.25s
After: 18.89s
17% faster
Signed-off-by: Anton Blanchard <anton at samba.org>
---
Index: linux-build/arch/powerpc/lib/copypage_power7.S
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-build/arch/powerpc/lib/copypage_power7.S 2012-05-30 14:20:32.457035092 +1000
@@ -0,0 +1,168 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2012
+ *
+ * Author: Anton Blanchard <anton at au.ibm.com>
+ */
+#include <asm/page.h>
+#include <asm/ppc_asm.h>
+
+#define STACKFRAMESIZE 256
+#define STK_REG(i) (112 + ((i)-14)*8)
+
+_GLOBAL(copypage_power7)
+ /*
+ * We prefetch both the source and destination using enhanced touch
+ * instructions. We use a stream ID of 0 for the load side and
+ * 1 for the store side. Since source and destination are page
+ * aligned we don't need to clear the bottom 7 bits of either
+ * address.
+ */
+ ori r9,r3,1 /* stream=1 */
+
+#ifdef CONFIG_PPC_64K_PAGES
+ lis r7,0x0E01 /* depth=7, units=512 */
+#else
+ lis r7,0x0E00 /* depth=7 */
+ ori r7,r7,0x1000 /* units=32 */
+#endif
+ ori r10,r7,1 /* stream=1 */
+
+ lis r8,0x8000 /* GO=1 */
+ clrldi r8,r8,32
+
+.machine push
+.machine "power4"
+ dcbt r0,r4,0b01000
+ dcbt r0,r7,0b01010
+ dcbtst r0,r9,0b01000
+ dcbtst r0,r10,0b01010
+ eieio
+ dcbt r0,r8,0b01010 /* GO */
+.machine pop
+
+#ifdef CONFIG_ALTIVEC
+ mflr r0
+ std r3,48(r1)
+ std r4,56(r1)
+ std r0,16(r1)
+ stdu r1,-STACKFRAMESIZE(r1)
+ bl .enter_vmx_copy
+ cmpwi r3,0
+ ld r0,STACKFRAMESIZE+16(r1)
+ ld r3,STACKFRAMESIZE+48(r1)
+ ld r4,STACKFRAMESIZE+56(r1)
+ mtlr r0
+
+ li r0,(PAGE_SIZE/128)
+ mtctr r0
+
+ beq .Lnonvmx_copy
+
+ addi r1,r1,STACKFRAMESIZE
+
+ li r6,16
+ li r7,32
+ li r8,48
+ li r9,64
+ li r10,80
+ li r11,96
+ li r12,112
+
+ .align 5
+1: lvx vr7,r0,r4
+ lvx vr6,r4,r6
+ lvx vr5,r4,r7
+ lvx vr4,r4,r8
+ lvx vr3,r4,r9
+ lvx vr2,r4,r10
+ lvx vr1,r4,r11
+ lvx vr0,r4,r12
+ addi r4,r4,128
+ stvx vr7,r0,r3
+ stvx vr6,r3,r6
+ stvx vr5,r3,r7
+ stvx vr4,r3,r8
+ stvx vr3,r3,r9
+ stvx vr2,r3,r10
+ stvx vr1,r3,r11
+ stvx vr0,r3,r12
+ addi r3,r3,128
+ bdnz 1b
+
+ b .exit_vmx_copy /* tail call optimise */
+
+#else
+ li r0,(PAGE_SIZE/128)
+ mtctr r0
+
+ stdu r1,-STACKFRAMESIZE(r1)
+#endif
+
+.Lnonvmx_copy:
+ std r14,STK_REG(r14)(r1)
+ std r15,STK_REG(r15)(r1)
+ std r16,STK_REG(r16)(r1)
+ std r17,STK_REG(r17)(r1)
+ std r18,STK_REG(r18)(r1)
+ std r19,STK_REG(r19)(r1)
+ std r20,STK_REG(r20)(r1)
+
+1: ld r0,0(r4)
+ ld r5,8(r4)
+ ld r6,16(r4)
+ ld r7,24(r4)
+ ld r8,32(r4)
+ ld r9,40(r4)
+ ld r10,48(r4)
+ ld r11,56(r4)
+ ld r12,64(r4)
+ ld r14,72(r4)
+ ld r15,80(r4)
+ ld r16,88(r4)
+ ld r17,96(r4)
+ ld r18,104(r4)
+ ld r19,112(r4)
+ ld r20,120(r4)
+ addi r4,r4,128
+ std r0,0(r3)
+ std r5,8(r3)
+ std r6,16(r3)
+ std r7,24(r3)
+ std r8,32(r3)
+ std r9,40(r3)
+ std r10,48(r3)
+ std r11,56(r3)
+ std r12,64(r3)
+ std r14,72(r3)
+ std r15,80(r3)
+ std r16,88(r3)
+ std r17,96(r3)
+ std r18,104(r3)
+ std r19,112(r3)
+ std r20,120(r3)
+ addi r3,r3,128
+ bdnz 1b
+
+ ld r14,STK_REG(r14)(r1)
+ ld r15,STK_REG(r15)(r1)
+ ld r16,STK_REG(r16)(r1)
+ ld r17,STK_REG(r17)(r1)
+ ld r18,STK_REG(r18)(r1)
+ ld r19,STK_REG(r19)(r1)
+ ld r20,STK_REG(r20)(r1)
+ addi r1,r1,STACKFRAMESIZE
+ blr
Index: linux-build/arch/powerpc/lib/Makefile
===================================================================
--- linux-build.orig/arch/powerpc/lib/Makefile 2012-05-30 10:53:03.442309322 +1000
+++ linux-build/arch/powerpc/lib/Makefile 2012-05-30 11:07:54.361827650 +1000
@@ -17,7 +17,7 @@ obj-$(CONFIG_HAS_IOMEM) += devres.o
obj-$(CONFIG_PPC64) += copypage_64.o copyuser_64.o \
memcpy_64.o usercopy_64.o mem_64.o string.o \
checksum_wrappers_64.o hweight_64.o \
- copyuser_power7.o string_64.o
+ copyuser_power7.o string_64.o copypage_power7.o
obj-$(CONFIG_XMON) += sstep.o ldstfp.o
obj-$(CONFIG_KPROBES) += sstep.o ldstfp.o
obj-$(CONFIG_HAVE_HW_BREAKPOINT) += sstep.o ldstfp.o
Index: linux-build/arch/powerpc/lib/copypage_64.S
===================================================================
--- linux-build.orig/arch/powerpc/lib/copypage_64.S 2012-05-30 10:53:03.430309112 +1000
+++ linux-build/arch/powerpc/lib/copypage_64.S 2012-05-30 11:07:54.361827650 +1000
@@ -17,7 +17,11 @@ PPC64_CACHES:
.section ".text"
_GLOBAL(copy_page)
+BEGIN_FTR_SECTION
lis r5,PAGE_SIZE at h
+FTR_SECTION_ELSE
+ b .copypage_power7
+ALT_FTR_SECTION_END_IFCLR(CPU_FTR_VMX_COPY)
ori r5,r5,PAGE_SIZE at l
BEGIN_FTR_SECTION
ld r10,PPC64_CACHES at toc(r2)
Index: linux-build/arch/powerpc/lib/vmx-helper.c
===================================================================
--- linux-build.orig/arch/powerpc/lib/vmx-helper.c 2012-05-30 10:53:03.454309531 +1000
+++ linux-build/arch/powerpc/lib/vmx-helper.c 2012-05-30 14:20:38.637144276 +1000
@@ -49,3 +49,26 @@ int exit_vmx_usercopy(void)
pagefault_enable();
return 0;
}
+
+int enter_vmx_copy(void)
+{
+ if (in_interrupt())
+ return 0;
+
+ preempt_disable();
+
+ enable_kernel_altivec();
+
+ return 1;
+}
+
+/*
+ * All calls to this function will be optimised into tail calls. We are
+ * passed a pointer to the destination which we return as required by a
+ * memcpy implementation.
+ */
+void *exit_vmx_copy(void *dest)
+{
+ preempt_enable();
+ return dest;
+}
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