RE: [PATCH V2 -tip] lib,x86_64: improve the performance of memcpy() for unaligned copy

Ma, Ling
2010-10-08T07:43:45Z

Could you please give us full address for each comparison result,we will do some tests on my machine.
For unaligned cases older cpus will crossing cache line and slow down caused by load and store, but for nhm, no necessary to care about it.
By the way in kernel 64bit mode, our access mode should be around 8byte aligned.

Thanks
Ling

> -----Original Message-----
> From: Miao Xie [mailto:miaox@cn.fujitsu.com]
> Sent: Friday, October 08, 2010 3:28 PM
> To: Ingo Molnar; Andi Kleen; Ma, Ling; H. Peter Anvin; Thomas Gleixner; Zhao,
> Yakui
> Cc: Linux Kernel
> Subject: [PATCH V2 -tip] lib,x86_64: improve the performance of memcpy() for
> unaligned copy
>
> memcpy of x86_64 hasn't been optimized for the unaligned copy like other
> architecture, this patch fixed this problem.
>
> I have tested this patch by my benchmark tool(doing 500 bytes memory copy
> for 5,000,000 times)with various alignments and buffer sizes on my Core2
> box.
>
> Len Src/Dst Old memcpy New memcpy
> align
> --- ------- ------------- -------------
> 1 0/0 0s 47015us 0s 28265us
> 1 0/4 0s 28201us 0s 28199us
> 1 4/0 0s 28200us 0s 28199us
> 1 4/4 0s 28199us 0s 28206us
> 7 0/0 0s 24441us 0s 24438us
> 7 0/4 0s 24439us 0s 24438us
> 7 4/0 0s 24439us 0s 24438us
> 7 4/4 0s 24439us 0s 24439us
> 8 0/0 0s 20699us 0s 20687us
> 8 0/4 0s 20689us 0s 20901us
> 8 4/0 0s 20692us 0s 20679us
> 8 4/4 0s 20679us 0s 20679us
> 16 0/0 0s 18807us 0s 18802us
> 16 0/4 0s 26319us 0s 18800us
> 16 4/0 0s 18800us 0s 18806us
> 16 4/4 0s 26317us 0s 18803us
> 32 0/0 0s 35728us 0s 18800us
> 32 0/4 0s 35716us 0s 18800us
> 32 4/0 0s 35717us 0s 18800us
> 32 4/4 0s 35724us 0s 18803us
> 48 0/0 0s 26897us 0s 30080us
> 48 0/4 0s 33837us 0s 33838us
> 48 4/0 0s 27600us 0s 30079us
> 48 4/4 0s 30087us 0s 33854us
> 64 0/0 0s 41369us 0s 45115us
> 64 0/4 0s 62042us 0s 65800us
> 64 4/0 0s 56400us 0s 58278us
> 64 4/4 0s 84596us 0s 84606us
> 80 0/0 0s 35877us 0s 37611us
> 80 0/4 0s 77083us 0s 56404us
> 80 4/0 0s 52652us 0s 55611us
> 80 4/4 0s 75200us 0s 78968us
> 128 0/0 0s 52642us 0s 56403us
> 128 0/4 0s 95883us 0s 95891us
> 128 4/0 0s 114683us 0s 108511us
> 128 4/4 0s 144780us 0s 110927us
> 256 0/0 0s 80832us 0s 86489us
> 256 0/4 0s 178586us 0s 163562us
> 256 4/0 0s 208670us 0s 181719us
> 256 4/4 0s 270705us 0s 148525us
> 512 0/0 0s 156049us 0s 148348us
> 512 0/4 0s 313933us 0s 298908us
> 512 4/0 0s 411671us 0s 329025us
> 512 4/4 0s 516971us 0s 208746us
> 1024 0/0 0s 297067us 0s 274019us
> 1024 0/4 0s 584703us 0s 569604us
> 1024 4/0 0s 818104us 0s 616419us
> 1024 4/4 1s 22839us 0s 328953us
> 2048 0/0 0s 577077us 0s 524148us
> 2048 0/4 1s 125953us 1s 111258us
> 2048 4/0 1s 894000us 1s 202724us
> 2048 4/4 2s 331807us 0s 822437us
> 4096 0/0 1s 25881us 1s 34128us
> 4096 0/4 2s 619273us 2s 606489us
> 4096 4/0 3s 553989us 2s 390272us
> 4096 4/4 4s 737789us 1s 433213us
>
> Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
> ---
> arch/x86/lib/memcpy_64.S | 135
> +++++++++++++++++++++++++++++++++++++++++++++-
> 1 files changed, 134 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S
> index 75ef61e..b0224f8 100644
> --- a/arch/x86/lib/memcpy_64.S
> +++ b/arch/x86/lib/memcpy_64.S
> @@ -46,9 +46,39 @@ ENTRY(memcpy)
> * Use 32bit CMP here to avoid long NOP padding.
> */
> cmp $0x20, %edx
> - jb .Lhandle_tail
> + jbe .Lhandle_tail
>
> /*
> + * the code for unaligned copy is good for large-size copy(>100),
> + * so if the size is small, we needn't check dst and src is aligned
> + * or not.
> + */
> + cmp $100, %edx
> + jb .Lboth_aligned
> +
> + /*
> + * unaligned access always leads to bad performance, so in order to
> + * avoid unaligned access, we align the address(both src and dest)
> + * first, and then copy from a aligned src to an aligned dst by using
> + * shifts.
> + * But we found if src is aligned, although dest is unaligned, the
> + * performance of generic memory copy (That is reading data aligned
> + * from the source and writing data unaligned to the dest) is better
> + * than the one that uses shifts to avoid unaligned access.
> + * So if src is aligned, we needn't check dest is aligned or not, just
> + * goto .Lboth_aligned
> + */
> + test $7, %esi /* src align check */
> + jz .Lboth_aligned
> +
> + /* if dest and src both are unaligned, goto unaligned copy */
> + test $7, %edi
> + jnz .Ldst_unaligned
> +
> + jmp .Lsrc_unaligned_dst_aligned
> +
> +.Lboth_aligned:
> + /*
> * We check whether memory false dependece could occur,
> * then jump to corresponding copy mode.
> */
> @@ -166,6 +196,109 @@ ENTRY(memcpy)
>
> .Lend:
> retq
> +
> + .p2align 4
> +.Ldst_unaligned:
> + movq %rdi, %rcx
> + andq $7, %rcx /* Align the destination */
> + negq %rcx
> + andq $7, %rcx
> + subq %rcx, %rdx
> +
> + /* tune dst address */
> + movq (%rsi), %r8
> + movq %r8, (%rdi)
> + addq %rcx, %rdi
> + addq %rcx, %rsi
> +
> + test $7, %esi /* src align check */
> + jz .Lboth_aligned
> +
> + .p2align 4
> +.Lsrc_unaligned_dst_aligned:
> + push %rbx
> + push %r12
> + push %r13
> + push %r14
> + push %r15
> + /*
> + * Calculate how to shift a word read at the memory operation
> + * aligned srcp to make it aligned for copy.
> + */
> + movq %rsi, %r14
> + andq $7, %r14
> + shlq $3, %r14
> +
> + movq $64, %r15
> + subq %r14, %r15
> +
> + andq $-8, %rsi /* src aligned */
> + movq 0*8(%rsi), %r8
> +
> + movq %rdx, %rbx
> + shrq $5, %rbx
> + jz .Lsrc_unaligned_less32
> +
> + /*
> + * %r8 : store src[0]
> + * %r9 : store src[1]
> + * %r10: store src[2]
> + * %r11: store src[3]
> + * %r12: store src[4]
> + * %r13: store the tmp data
> + */
> + .p2align 4
> +.Lsrc_unaligned_loop32:
> + movq 1*8(%rsi), %r9
> + movq 2*8(%rsi), %r10
> + movq 3*8(%rsi), %r11
> + movq 4*8(%rsi), %r12
> +
> + movq %r9, %r13
> + movb %r14b, %cl
> + shrq %cl, %r8
> + shrq %cl, %r13
> + movb %r15b, %cl
> + shlq %cl, %r9
> + orq %r8, %r9
> + movq %r10, %r8
> + shlq %cl, %r10
> + orq %r13, %r10
> +
> + movq %r11, %r13
> + movb %r14b, %cl
> + shrq %cl, %r8
> + shrq %cl, %r13
> + movb %r15b, %cl
> + shlq %cl, %r11
> + orq %r8, %r11
> + movq %r12, %r8
> + shlq %cl, %r12
> + orq %r13, %r12
> +
> + movq %r9, 0*8(%rdi)
> + movq %r10, 1*8(%rdi)
> + movq %r11, 2*8(%rdi)
> + movq %r12, 3*8(%rdi)
> +
> + leaq 4*8(%rdi), %rdi
> + leaq 4*8(%rsi), %rsi
> + decq %rbx
> + jnz .Lsrc_unaligned_loop32
> +
> + .p2align 4
> +.Lsrc_unaligned_less32:
> + shrq $3, %r14
> + addq %r14, %rsi
> + pop %r15
> + pop %r14
> + pop %r13
> + pop %r12
> + pop %rbx
> + andq $31, %rdx
> + jnz .Lhandle_tail
> + retq
> +
> CFI_ENDPROC
> ENDPROC(memcpy)
> ENDPROC(__memcpy)
> --
> 1.7.0.1