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Message-Id: <e7c3b265254b705286f1.1166032640@eng-12.pathscale.com> Date: Wed, 13 Dec 2006 09:57:20 -0700 From: Bryan O'Sullivan <bos@...hscale.com> To: akpm@...l.org Cc: linux-kernel@...r.kernel.org, openib-general@...nib.org Subject: [PATCH 1 of 2] Add memcpy_uncached_read, a memcpy that tries to reduce cache pressure This copy routine is memcpy-compatible, but on some architectures will use cache-bypassing loads to avoid bringing the source data into the cache. One case where this is useful is when a device issues a DMA to a memory region, and the CPU must copy the DMAed data elsewhere before doing any work with it. Since the source data is read-once, write-never from the CPU's perspective, caching the data at those addresses can only evict potentially useful data. We provide an x86_64 implementation that uses SSE non-temporal loads, and a generic version that falls back to plain memcpy. Implementors for other arches should not use cache-bypassing stores to the destination, as in most cases, the destination is accessed almost immediately after a copy finishes. Signed-off-by: Bryan O'Sullivan <bryan.osullivan@...gic.com> diff -r 4a0c3ede5076 -r e7c3b265254b arch/x86_64/lib/Makefile --- a/arch/x86_64/lib/Makefile Tue Dec 12 10:43:21 2006 -0800 +++ b/arch/x86_64/lib/Makefile Wed Dec 13 09:51:09 2006 -0800 @@ -9,4 +9,5 @@ lib-y := csum-partial.o csum-copy.o csum lib-y := csum-partial.o csum-copy.o csum-wrappers.o delay.o \ usercopy.o getuser.o putuser.o \ thunk.o clear_page.o copy_page.o bitstr.o bitops.o -lib-y += memcpy.o memmove.o memset.o copy_user.o rwlock.o +lib-y += memcpy.o memmove.o memset.o copy_user.o rwlock.o \ + memcpy_uncached_read.o diff -r 4a0c3ede5076 -r e7c3b265254b arch/x86_64/lib/memcpy_uncached_read.S --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/arch/x86_64/lib/memcpy_uncached_read.S Wed Dec 13 09:51:09 2006 -0800 @@ -0,0 +1,142 @@ +/* + * Copyright (c) 2006 QLogic Corporation. All Rights Reserved. + * + * This file is free software; you can redistribute it and/or modify + * it under the terms of version 2 of the GNU General Public License + * as published by the Free Software Foundation. + * + * 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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. + */ + +/* + * memcpy_uncached_read - memcpy-compatible copy routine, using streaming loads + * @dest: destination address + * @src: source address (will not be cached) + * @count: number of bytes to copy + * + * Use streaming loads and normal stores for a special-case copy where + * we know we won't be reading the source again, but will be reading the + * destination again soon. + */ + .text + .p2align 4,,15 + /* rdi destination, rsi source, rdx count */ + .globl memcpy_uncached_read + .type memcpy_uncached_read, @function +memcpy_uncached_read: + movq %rdi, %rax +.L5: + cmpq $15, %rdx + ja .L34 +.L3: + cmpl $8, %edx /* rdx is 0..15 */ + jbe .L9 +.L6: + testb $8, %dxl /* rdx is 3,5,6,7,9..15 */ + je .L13 + movq (%rsi), %rcx + addq $8, %rsi + movq %rcx, (%rdi) + addq $8, %rdi +.L13: + testb $4, %dxl + je .L15 + movl (%rsi), %ecx + addq $4, %rsi + movl %ecx, (%rdi) + addq $4, %rdi +.L15: + testb $2, %dxl + je .L17 + movzwl (%rsi), %ecx + addq $2, %rsi + movw %cx, (%rdi) + addq $2, %rdi +.L17: + testb $1, %dxl + je .L33 +.L1: + movzbl (%rsi), %ecx + movb %cl, (%rdi) +.L33: + ret +.L34: + cmpq $63, %rdx /* rdx is > 15 */ + ja .L64 + movl $16, %ecx /* rdx is 16..63 */ +.L25: + movq 8(%rsi), %r8 + movq (%rsi), %r9 + addq %rcx, %rsi + movq %r8, 8(%rdi) + movq %r9, (%rdi) + addq %rcx, %rdi + subq %rcx, %rdx + cmpl %edx, %ecx /* is rdx >= 16? */ + jbe .L25 + jmp .L3 /* rdx is 0..15 */ + .p2align 4,,7 +.L64: + movl $64, %ecx +.L42: + prefetchnta 128(%rsi) + movq (%rsi), %r8 + movq 8(%rsi), %r9 + movq 16(%rsi), %r10 + movq 24(%rsi), %r11 + subq %rcx, %rdx + movq %r8, (%rdi) + movq 32(%rsi), %r8 + movq %r9, 8(%rdi) + movq 40(%rsi), %r9 + movq %r10, 16(%rdi) + movq 48(%rsi), %r10 + movq %r11, 24(%rdi) + movq 56(%rsi), %r11 + addq %rcx, %rsi + movq %r8, 32(%rdi) + movq %r9, 40(%rdi) + movq %r10, 48(%rdi) + movq %r11, 56(%rdi) + addq %rcx, %rdi + cmpq %rdx, %rcx /* is rdx >= 64? */ + jbe .L42 + sfence + orl %edx, %edx + je .L33 + jmp .L5 +.L9: + jmp *.L12(,%rdx,8) /* rdx is 0..8 */ + .section .rodata + .align 8 + .align 4 +.L12: + .quad .L33 + .quad .L1 + .quad .L2 + .quad .L6 + .quad .L4 + .quad .L6 + .quad .L6 + .quad .L6 + .quad .L8 + .text +.L2: + movzwl (%rsi), %ecx + movw %cx, (%rdi) + ret +.L4: + movl (%rsi), %ecx + movl %ecx, (%rdi) + ret +.L8: + movq (%rsi), %rcx + movq %rcx, (%rdi) + ret diff -r 4a0c3ede5076 -r e7c3b265254b include/asm-x86_64/string.h --- a/include/asm-x86_64/string.h Tue Dec 12 10:43:21 2006 -0800 +++ b/include/asm-x86_64/string.h Wed Dec 13 09:51:09 2006 -0800 @@ -39,6 +39,8 @@ extern void *__memcpy(void *to, const vo __ret = __builtin_memcpy((dst),(src),__len); \ __ret; }) +#define __HAVE_ARCH_MEMCPY_UNCACHED_READ +extern void *memcpy_uncached_read(void *to, const void *from, size_t len); #define __HAVE_ARCH_MEMSET void *memset(void *s, int c, size_t n); diff -r 4a0c3ede5076 -r e7c3b265254b include/linux/string.h --- a/include/linux/string.h Tue Dec 12 10:43:21 2006 -0800 +++ b/include/linux/string.h Wed Dec 13 09:51:09 2006 -0800 @@ -85,6 +85,9 @@ extern void * memset(void *,int,__kernel #ifndef __HAVE_ARCH_MEMCPY extern void * memcpy(void *,const void *,__kernel_size_t); #endif +#ifndef __HAVE_ARCH_MEMCPY_UNCACHED_READ +#define memcpy_uncached_read(dest, src, count) memcpy((dest), (src), (count)) +#endif #ifndef __HAVE_ARCH_MEMMOVE extern void * memmove(void *,const void *,__kernel_size_t); #endif - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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