Re: Status of strchr

[Liubov Dmitrieva <liubov dot dmitrieva at gmail dot com>]

I've got results for atom and Silvermont, check it out.
I used http://kam.mff.cuni.cz/~ondra/benchmark_string/strchr_profile200813.tar.bz2


--
Liubov Dmitrieva

On Tue, Aug 20, 2013 at 8:34 PM, OndÅej BÃlka <neleai@seznam.cz> wrote:
> On Wed, Aug 14, 2013 at 10:37:24PM +0200, OndÅej BÃlka wrote:
>> On Wed, Aug 14, 2013 at 11:46:23AM +0400, Liubov Dmitrieva wrote:
>>
>> A problem here is that my 64-byte loop is after 512 characters fastest
>> but there is big constant overhead that makes 16-byte loop better at
>> that interval.
>>
>> It is partially caused by that I did not do much tuning to this
>> implementation. I wrote strchr_new_v2 that decreases overhead somewhat
>> but it has a catch.
>>
>>
>> It is possible, other variant is to write header that does not use
>> unaligned loads.
>>
>> It is not only problem of atom but also for old athlons a no-bsf variant
>> looks 10% faster than what is selected and my improvement.
>> http://kam.mff.cuni.cz/~ondra/benchmark_string/athlon_x2/strchr_profile/results_gcc/result.html
>>
>> A silvermont is problematic as problem looks to be in loop overhead. One
>> possibility is wait how optimized can 64-byte loop be.
>>
> That was v2.
>
>> A second possibility is also try a 32-byte loop and see how it fares.
>>
> Which I tried now. It does have smaller overhead except for 32-64 byte
> range. I want to see if it helps atom and silvermont.
>
>  http://kam.mff.cuni.cz/~ondra/benchmark_string/strchr_profile.html
>  http://kam.mff.cuni.cz/~ondra/benchmark_string/strchr_profile200813.tar.bz2
>
> It is also few percent faster in practice. However there is drawback
> that it is about 10% slower for sizes from 8000 bytes and more than
> 64-byte loop.
>
> Now I am inclined to make this default if you can cope with that
> tradeoff.
>
> # sse2 strchr_new_loop32 blue
>         .file   "strchr_pair.c"
>         .text
>         .p2align 4,,15
> .globl strchr_new_loop32
>         .type   strchr_new_loop32, @function
> strchr_new_loop32:
> .LFB519:
>         .cfi_startproc
>         movd    %esi, %xmm3
>         movl    %edi, %eax
>         andl    $4095, %eax
>         punpcklbw       %xmm3, %xmm3
>         cmpl    $4063, %eax
>         punpcklwd       %xmm3, %xmm3
>         pshufd  $0, %xmm3, %xmm3
>         jg      .L11
>         movdqu  (%rdi), %xmm1
>         pxor    %xmm2, %xmm2
>         movdqa  %xmm3, %xmm0
>         movdqa  %xmm1, %xmm4
>         pcmpeqb %xmm3, %xmm1
>         pcmpeqb %xmm2, %xmm4
>         por     %xmm4, %xmm1
>         pmovmskb        %xmm1, %edx
>         movdqu  16(%rdi), %xmm1
>         pcmpeqb %xmm1, %xmm2
>         pcmpeqb %xmm1, %xmm0
>         por     %xmm2, %xmm0
>         pmovmskb        %xmm0, %eax
>         salq    $16, %rax
>         orq     %rdx, %rax
>         jne     .L9
> .L3:
>         pxor    %xmm5, %xmm5
>         andq    $-32, %rdi
>         .p2align 4,,10
>         .p2align 3
> .L6:
>         addq    $32, %rdi
>         movdqa  (%rdi), %xmm1
>         movdqa  16(%rdi), %xmm0
>         pxor    %xmm3, %xmm1
>         pxor    %xmm3, %xmm0
>         pminub  (%rdi), %xmm1
>         pminub  16(%rdi), %xmm0
>         pminub  %xmm1, %xmm0
>         pcmpeqb %xmm5, %xmm0
>         pmovmskb        %xmm0, %eax
>         testl   %eax, %eax
>         je      .L6
>         movdqa  16(%rdi), %xmm0
>         pcmpeqb %xmm5, %xmm1
>         pcmpeqb %xmm0, %xmm3
>         pcmpeqb %xmm5, %xmm0
>         por     %xmm3, %xmm0
>         pmovmskb        %xmm1, %edx
>         pmovmskb        %xmm0, %eax
>         salq    $16, %rax
>         orq     %rdx, %rax
> .L9:
>         bsf     %eax, %eax
>         movl    $0, %edx
>         leaq    (%rdi,%rax), %rax
>         cmpb    %sil, (%rax)
>         cmovne  %rdx, %rax
>         ret
>         .p2align 4,,10
>         .p2align 3
> .L11:
>         movq    %rdi, %rdx
>         pxor    %xmm2, %xmm2
>         andq    $-32, %rdx
>         movdqa  %xmm3, %xmm0
>         movdqa  (%rdx), %xmm1
>         movdqa  %xmm1, %xmm4
>         pcmpeqb %xmm3, %xmm1
>         pcmpeqb %xmm2, %xmm4
>         por     %xmm4, %xmm1
>         pmovmskb        %xmm1, %ecx
>         movdqa  16(%rdx), %xmm1
>         pcmpeqb %xmm1, %xmm2
>         pcmpeqb %xmm1, %xmm0
>         por     %xmm2, %xmm0
>         pmovmskb        %xmm0, %eax
>         salq    $16, %rax
>         orq     %rcx, %rax
>         movl    %edi, %ecx
>         subb    %dl, %cl
>         shrq    %cl, %rax
>         testq   %rax, %rax
>         je      .L3
>         jmp     .L9
>         .cfi_endproc
> .LFE519:
>         .size   strchr_new_loop32, .-strchr_new_loop32
>         .ident  "GCC: (Debian 4.5.3-12) 4.5.3"
>         .section        .note.GNU-stack,"",@progbits

Attachment: results_strchr_atom_2008.tar.bz2
Description: BZip2 compressed data

Attachment: results_strchr_silvermont_2008.tar.bz2
Description: BZip2 compressed data