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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji

which is the fastest ?

edit:
not :mov qword[edi],mm1
but :movq qword[edi],mm1


Code:
     xor eax,eax
     mov ecx,Y

A :  stosd
     loop A

;------------------------ or

     xor eax,eax
     movd mm1,eax
     mov ecx,Y/2

B:   mov qword[edi],mm1
     add edi,8
     loop B

     (emms)
    

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Last edited by ouadji on 20 Sep 2010, 21:06; edited 1 time in total
Post 20 Sep 2010, 20:20
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Fanael



Joined: 03 Jul 2009
Posts: 168
Fanael
As usual - it depends upon what CPU are you optimizing for (and upon several other things, also).
Post 20 Sep 2010, 20:23
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edfed



Joined: 20 Feb 2006
Posts: 4242
Location: 2018
edfed
you can also make this:

Code:
xor ax,eax
mov ecx,Y/2
A:
stosd
stosd
loop A:
    


or

Code:
xor eax,eax
mov ecx,Y
rep stosd
    


i believe that the faster is to do it with only one instruction. with rep prefix.

i will compare it right now and give feedback
Post 20 Sep 2010, 20:46
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ouadji



Joined: 24 Dec 2008
Posts: 1081
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ouadji
Quote:
i will compare it right now and give feedback
thank you edfed

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Post 20 Sep 2010, 20:50
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edfed



Joined: 20 Feb 2006
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edfed
mov qword[edi],mm1 doesn't compile.
Post 20 Sep 2010, 21:01
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji

not "mov" ... but "movq"

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Post 20 Sep 2010, 21:05
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edfed



Joined: 20 Feb 2006
Posts: 4242
Location: 2018
edfed
i have results.
the faster on my PIII is test1 (~1180 clocks).
test 3 is a little slower (~1260clocks), and test2 is twice slower (~2200 clocks).

Code:
X:
Y=10h
rd Y*2

@@: db 'test1',0
align 4
dd test1.size
dd @b
test1:
     xor eax,eax
     mov edi,X
     mov ecx,Y
@@:  stosd
     loop @b
.size=$-test1
     mov eax,0
     ret
;------------------------
@@: db 'test2',0
align 4
dd test2.size
dd @b
test2:
     xor eax,eax
     movd mm1,eax
     mov edi,X
     mov ecx,Y/2
@@:  movq [edi],mm1
     add edi,8
     loop @b
.size= $-test2
     mov eax,0
     ret
;------------------------

@@: db 'test3',0
align 4
dd test3.size
dd @b
Y=10h
test3:
     xor eax,eax
     mov edi,X
     mov ecx,Y
     rep stosd
.size=$-test1
     mov eax,0
     ret
;------------------------
    
Post 20 Sep 2010, 21:16
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji

surprising result (thank you edfed)
"loop" is faster than "rep" ...
and regarding "movq/mm1", we forget that!

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Post 20 Sep 2010, 21:43
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edfed



Joined: 20 Feb 2006
Posts: 4242
Location: 2018
edfed
there are many things to take in consideration.
the fat that we write to ES, and ES is the video memory in my test application.

the fact that the buffer is only 10 dwords.
and many other things.

but i am really sure when i say test1 is relativelly the faster.

[edit]
but, i just tested with 100 dwords, and test3 becomes the faster.

[edit1]
but i tested with CPU overloaded, and MMX is faster.

as a conclusion, a short table should use test1 (loop), a medium table use test3 (rep), and a long table use test2(mmx).
Post 20 Sep 2010, 21:51
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17667
Location: In your JS exploiting you and your system
revolution
Testing for speed on a single CPU with a single test and one test set over a short run is rather pointless.
Post 20 Sep 2010, 23:14
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edfed



Joined: 20 Feb 2006
Posts: 4242
Location: 2018
edfed
but very interresting.
many things are deveiled by the time capture, and scroll the plotted results.
it shows many interactions with the real state of the machine.
Smile

i correct, test3 is the faster. and the difference is huge.
test3 = 500 clocks, test1 = 2500 clocks, test2 = 2700

it really depends on the load of the machine, it is interresting to see that an algorythm can be influenced by the rest of the system.
Post 20 Sep 2010, 23:46
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji

This final results seem rather logical.
The test3 is the only one with which the loop is performed inside the processor.
Thank you edfed for all tests and results.

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Post 21 Sep 2010, 07:42
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edfed



Joined: 20 Feb 2006
Posts: 4242
Location: 2018
edfed
then, a capture of the results.
Image

alternates test1, test2, test3 and test4
test 3 = lower plots, test 1 = higher plots.

then, even it doesn't give absolute results, it gives a good idea of relative speed between several methods.

i am currently trying to simplify the process, because for the moment, it is only a compile time application that needs this kind of implementation:
Code:
align 4
.list:  List \
        test1,\
        test2,\
        test3,\
        test4

Y=100h
X:
rd Y*2

@@: db 'test1',0
align 4
dd test1.size
dd @b
test1:
     xor eax,eax
     mov edi,X
     mov ecx,Y
@@:  stosd
     loop @b
.size=$-test1
     mov eax,0
     ret
;------------------------
@@: db 'test2',0
align 4
dd test2.size
dd @b
test2:
     xor eax,eax
     movd mm1,eax
     mov edi,X
     mov ecx,Y/2
@@:  movq [es:edi],mm1
     add edi,8
     loop @b
.size= $-test2
     mov eax,0
     ret
;------------------------

@@: db 'test3',0
align 4
dd test3.size
dd @b
test3:
     xor eax,eax
     mov edi,X
     mov ecx,Y
     rep stosd
.size=$-test3
     mov eax,0
     ret
;------------------------

@@: db 'test4',0
align 4
dd test4.size
dd @b
test4:
     xor eax,eax
     mov edi,X
     mov ecx,Y
@@:  mov [es:edi],eax
     add edi,4
     loop @b
.size=$-test4
     mov eax,0
     ret
;------------------------

    


maybe a .bin include at load time is better.
compile each snippet in .bin, with org 0
just reference them in a list of paths, at compile time, or at execution time with a command line, and then, begin the test???


Description:
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Viewed: 6340 Time(s)

tricktest.png


Post 23 Sep 2010, 10:34
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji

great result edfed, good work.

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Post 23 Sep 2010, 13:49
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bitRAKE



Joined: 21 Jul 2003
Posts: 3045
Location: vpcmipstrm
bitRAKE
Code:
test8:
     pxor mm0,mm0
     mov edi,X
     mov ecx,Y/2
@@:  movntq [es:edi+ecx*8-8],mm0
     loop @b
     ret


test9:
     pxor xmm0,xmm0
     mov edi,X
     mov ecx,Y/4
@@:  movntdq [es:edi],xmm0
     add edi,16
     loop @b
     ret    
These might only be useful for larger blocks - haven't tested. It's also important if the memory will be used soon after clearing - if so, then non-temporal stores should be avoided. Of course, SSE2 is needed.
Post 24 Sep 2010, 01:06
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji

I'd be interested to know the test9 result
thank you edfed

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Post 24 Sep 2010, 12:55
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edfed



Joined: 20 Feb 2006
Posts: 4242
Location: 2018
edfed
from what i see, i can say that test9 is not working properlly, but as i am not sure to have SSE2 on my PIII, i am not sure of the exact result.

you can test yourself on your machine if you want.

i renamed test9, it is now test5.
i didn't included test8 because it looks like the mmx solution in test2


Last edited by edfed on 24 Sep 2010, 19:38; edited 1 time in total
Post 24 Sep 2010, 19:09
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji

Sorry for this reply in french, to complex for me in english.

Edfed, j'ai testé sur mon PC. C'est un 4 coeurs Q6600 sous XP pro.
Je peux sélectionner les tests avec les flèches haut et bas, mais quand je dépasse "test4" le programme se ferme de lui même. Je n'ai donc pas eu accès à votre "test5", dommage !

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Post 24 Sep 2010, 19:22
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edfed



Joined: 20 Feb 2006
Posts: 4242
Location: 2018
edfed
ok, it means that you don't support sse2. lol. but j'ai des doutes. faudrait voir si ce n'est pas le système qui bloque l'utilisation de ce jeux d'instruction en mode dos.

i think you will need to test it with an other type of code. for example just test it in a PE console code instead of .com

hem. i think the problem come form the use of CPUID in test9.

i will correct it and post a new version.

but i propose you to directlly compile my source after adding your own tests.


Description:
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Filename: B2h.zip
Filesize: 16.25 KB
Downloaded: 140 Time(s)



Last edited by edfed on 28 Feb 2011, 14:06; edited 1 time in total
Post 24 Sep 2010, 19:31
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji

Q6600 does not support sse2 ?

avx ,d'accord, mais sse2 ?
j'espère quand même "que oui" ... !
(j'ai un marteau juste à côté du PC) Crying or Very sad

ps: no source, only a" file.com"

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Post 24 Sep 2010, 20:18
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