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powerpc: POWER7 optimised copy_page using VMX and enhanced prefetch

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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@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Anton Blanchard 2012-05-29 19:33:12 +00:00 committed by Benjamin Herrenschmidt
parent 6f7839e542
commit fde69282b7
4 changed files with 196 additions and 1 deletions
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2
arch/powerpc/lib/Makefile
View file

@ -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

4
arch/powerpc/lib/copypage_64.S
View file

@ -17,7 +17,11 @@ PPC64_CACHES:
.section ".text"
_GLOBAL(copy_page)
BEGIN_FTR_SECTION
lis r5,PAGE_SIZE@h
FTR_SECTION_ELSE
b .copypage_power7
ALT_FTR_SECTION_END_IFCLR(CPU_FTR_VMX_COPY)
ori r5,r5,PAGE_SIZE@l
BEGIN_FTR_SECTION
ld r10,PPC64_CACHES@toc(r2)

168
arch/powerpc/lib/copypage_power7.S Normal file
View file

@ -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@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

23
arch/powerpc/lib/vmx-helper.c
View file

@ -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;
}