powerpc: 64bit optimised __clear_user

I noticed __clear_user high up in a profile of one of my RAID stress
tests. The testcase was doing a dd from /dev/zero which ends up
calling __clear_user.

__clear_user is basically a loop with a single 4 byte store which
is horribly slow. We can do much better by aligning the desination
and doing 32 bytes of 8 byte stores in a loop.

The following testcase was used to verify the patch:

http://ozlabs.org/~anton/junkcode/stress_clear_user.c

To show the improvement in performance I ran a dd from /dev/zero
to /dev/null on a POWER7 box:

Before:

# dd if=/dev/zero of=/dev/null bs=1M count=10000
10485760000 bytes (10 GB) copied, 3.72379 s, 2.8 GB/s

After:

# time dd if=/dev/zero of=/dev/null bs=1M count=10000
10485760000 bytes (10 GB) copied, 0.728318 s, 14.4 GB/s

Over 5x 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 2012-05-27 19:54:03 +00:00 committed by Benjamin Herrenschmidt
parent d136e27326
commit 17968fbbd1
3 changed files with 144 additions and 1 deletions

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
copyuser_power7.o string_64.o
obj-$(CONFIG_XMON) += sstep.o ldstfp.o
obj-$(CONFIG_KPROBES) += sstep.o ldstfp.o
obj-$(CONFIG_HAVE_HW_BREAKPOINT) += sstep.o ldstfp.o

View File

@ -119,6 +119,7 @@ _GLOBAL(memchr)
2: li r3,0
blr
#ifdef CONFIG_PPC32
_GLOBAL(__clear_user)
addi r6,r3,-4
li r3,0
@ -160,3 +161,4 @@ _GLOBAL(__clear_user)
PPC_LONG 1b,91b
PPC_LONG 8b,92b
.text
#endif

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@ -0,0 +1,141 @@
/*
* 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/ppc_asm.h>
/**
* __clear_user: - Zero a block of memory in user space, with less checking.
* @to: Destination address, in user space.
* @n: Number of bytes to zero.
*
* Zero a block of memory in user space. Caller must check
* the specified block with access_ok() before calling this function.
*
* Returns number of bytes that could not be cleared.
* On success, this will be zero.
*/
.macro err1
100:
.section __ex_table,"a"
.align 3
.llong 100b,.Ldo_err1
.previous
.endm
.macro err2
200:
.section __ex_table,"a"
.align 3
.llong 200b,.Ldo_err2
.previous
.endm
.macro err3
300:
.section __ex_table,"a"
.align 3
.llong 300b,.Ldo_err3
.previous
.endm
.Ldo_err1:
mr r3,r8
.Ldo_err2:
mtctr r4
1:
err3; stb r0,0(r3)
addi r3,r3,1
addi r4,r4,-1
bdnz 1b
.Ldo_err3:
mr r3,r4
blr
_GLOBAL(__clear_user)
cmpdi r4,32
neg r6,r3
li r0,0
blt .Lshort_clear
mr r8,r3
mtocrf 0x01,r6
clrldi r6,r6,(64-3)
/* Get the destination 8 byte aligned */
bf cr7*4+3,1f
err1; stb r0,0(r3)
addi r3,r3,1
1: bf cr7*4+2,2f
err1; sth r0,0(r3)
addi r3,r3,2
2: bf cr7*4+1,3f
err1; stw r0,0(r3)
addi r3,r3,4
3: sub r4,r4,r6
srdi r6,r4,5
cmpdi r4,32
blt .Lshort_clear
mtctr r6
/* Do 32 byte chunks */
4:
err2; std r0,0(r3)
err2; std r0,8(r3)
err2; std r0,16(r3)
err2; std r0,24(r3)
addi r3,r3,32
addi r4,r4,-32
bdnz 4b
.Lshort_clear:
/* up to 31 bytes to go */
cmpdi r4,16
blt 6f
err2; std r0,0(r3)
err2; std r0,8(r3)
addi r3,r3,16
addi r4,r4,-16
/* Up to 15 bytes to go */
6: mr r8,r3
clrldi r4,r4,(64-4)
mtocrf 0x01,r4
bf cr7*4+0,7f
err1; std r0,0(r3)
addi r3,r3,8
7: bf cr7*4+1,8f
err1; stw r0,0(r3)
addi r3,r3,4
8: bf cr7*4+2,9f
err1; sth r0,0(r3)
addi r3,r3,2
9: bf cr7*4+3,10f
err1; stb r0,0(r3)
10: li r3,0
blr