What's your per iteration time?

hyh1048576 · 2003-06-21, 14:16

My CPU is Intel Celeron 1100Mhz and my per iteration time is 0.362s~0.372s.I used to have a P3 550Mhz,it's 0.502s~0.520s.It seems that it doesn't double the iteration speed when the CPU speed is doubled.But wpolly said his C4 2000Mhz CPU had 0.0608s~0.0618s!
WHY?????????Only CPU?Or I need to set something???
TELL ME WHY?

nomadicus · 2003-06-21, 15:43

hyh1048576,
P3's are more efficient per clock cycle then Celerons; so a switch from P3 to Celeron doesn't get you double the speed you expected. As to the P4 2GHz, that chip includes instructions that do not exist on Celerons (or P3's for that matter); prime95 takes advantage of these instructions and blows the doors off a comparable Celeron. In short prime95 is optimized for P4's because they have the HW instructions that previous chips (e.g., P3's and Celerons) don't have.
There are many posts throughout the forum that have more details.
-=- john

delta_t · 2003-06-21, 19:49

celerons also have smaller caches

hyh1048576 · 2003-06-22, 10:13

Thank you very much :D

QuintLeo · 2003-06-23, 01:53

I'd go with the cache size as the primary difference - PIII had a 256k cache IIRC in the 550s, vs. a 128K cache in the Celerons - this has a *major* effect on Prime, which is memory-intensive.

P-III 1100s have either a 256k or 512k cache (I believe the Tulatins started at either 1Ghz or 1.1Ghz) depending on the family. Your motherboard should support the 256K cache P-III, and might (check your manual and the web site for the manufacturer) support the 512K cache P-IIIs as well.

trif · 2003-06-23, 03:37

Quote:

Originally Posted by hyh1048576

My CPU is Intel Celeron 1100Mhz and my per iteration time is 0.362s~0.372s.I used to have a P3 550Mhz,it's 0.502s~0.520s.It seems that it doesn't double the iteration speed when the CPU speed is doubled.But wpolly said his C4 2000Mhz CPU had 0.0608s~0.0618s!
WHY?????????Only CPU?Or I need to set something???
TELL ME WHY?

It also depends on which exponent you are testing, and what FFT size it is using. The larger the FFT size, the longer the iteration time will be. So you need to be sure you are comparing iteration times from the same FFT size.

hyh1048576 · 2003-06-23, 12:48

ANOTHER QUESTION:
I realise that my Celeron 1100Mhz PC makes "per iteration time:0.320s"when 800*600 and"per iteration time:0.362s"when 1024*768.I wonder why------I'm going to try 640*480,1152*864 and 1280*1024.I'll send up my result tomorrow.

xtreme2k · 2003-06-23, 15:47

My guess is that your system uses an onboard video card which shares video memory with the system ram. This means when your video card needs to refresh something on the screen, system memory needs to be used for the operations. Basically this compete with the memory bandwidth used by the CPU.

Prime95 is a very memory bandwidth and latency sensitive program meaning anything that else that uses memory bandwidth while Prime95 is running run slows it down. Which is exactly what is happening in your case.

When you use a low resolution, eg 800x600, it uses less memory bandwidth to redraw the screen while you uses 1024x768 it uses much more memory bandwidth therefore slowing down Prime even more.

eepiccolo · 2003-06-23, 16:22

My computer at home uses the on-board video on the M-board. I'll have to fiddle around with it and see what happens.

hyh1048576 · 2003-06-24, 04:46

Hmm,here is my result:
colour 24bit 16bit 8bit(256 colour)
resolution
640*480 0.294 0.286 0.278
800*600 0.304 0.296 0.283
1024*768 0.328 0.307 0.291
1152*864 0.345 0.321 0.292
1280*1024 0.382 0.344 0.301
1600*1200 /////// /////// 0.319
********************************************
From 0.382 to 0.278,it can be 37% faster! MY GOD!I hope I have a 2-colour screen!.......
PS:Can the resolution be 1280*1024? I think it should be 1280*960,for the resolution is always 4k*3k,here k is integer.But the screen said so.

delta_t · 2003-06-24, 05:22

can you give us details of your computer?

2003-06-21, 14:16	#1
hyh1048576 Jun 2003 2⁶ Posts	What's your per iteration time? My CPU is Intel Celeron 1100Mhz and my per iteration time is 0.362s~0.372s.I used to have a P3 550Mhz,it's 0.502s~0.520s.It seems that it doesn't double the iteration speed when the CPU speed is doubled.But wpolly said his C4 2000Mhz CPU had 0.0608s~0.0618s! WHY?????????Only CPU?Or I need to set something??? TELL ME WHY?

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2003-06-21, 15:43	#2
nomadicus Jan 2003 North Carolina 2·3·41 Posts	hyh1048576, P3's are more efficient per clock cycle then Celerons; so a switch from P3 to Celeron doesn't get you double the speed you expected. As to the P4 2GHz, that chip includes instructions that do not exist on Celerons (or P3's for that matter); prime95 takes advantage of these instructions and blows the doors off a comparable Celeron. In short prime95 is optimized for P4's because they have the HW instructions that previous chips (e.g., P3's and Celerons) don't have. There are many posts throughout the forum that have more details. -=- john

2003-06-21, 19:49	#3
delta_t Nov 2002 Anchorage, AK 357₁₀ Posts	celerons also have smaller caches

2003-06-22, 10:13	#4
hyh1048576 Jun 2003 40₁₆ Posts	Thank you very much :D

2003-06-23, 01:53	#5
QuintLeo Oct 2002 Lost in the hills of Iowa 2⁶×7 Posts	I'd go with the cache size as the primary difference - PIII had a 256k cache IIRC in the 550s, vs. a 128K cache in the Celerons - this has a major effect on Prime, which is memory-intensive. P-III 1100s have either a 256k or 512k cache (I believe the Tulatins started at either 1Ghz or 1.1Ghz) depending on the family. Your motherboard should support the 256K cache P-III, and might (check your manual and the web site for the manufacturer) support the 512K cache P-IIIs as well.

2003-06-23, 12:48	#7
hyh1048576 Jun 2003 1000000₂ Posts	ANOTHER QUESTION: I realise that my Celeron 1100Mhz PC makes "per iteration time:0.320s"when 800600 and"per iteration time:0.362s"when 1024768.I wonder why------I'm going to try 640480,1152864 and 1280*1024.I'll send up my result tomorrow.

2003-06-23, 15:47	#8
xtreme2k Aug 2002 2×3×29 Posts	My guess is that your system uses an onboard video card which shares video memory with the system ram. This means when your video card needs to refresh something on the screen, system memory needs to be used for the operations. Basically this compete with the memory bandwidth used by the CPU. Prime95 is a very memory bandwidth and latency sensitive program meaning anything that else that uses memory bandwidth while Prime95 is running run slows it down. Which is exactly what is happening in your case. When you use a low resolution, eg 800x600, it uses less memory bandwidth to redraw the screen while you uses 1024x768 it uses much more memory bandwidth therefore slowing down Prime even more.

2003-06-23, 16:22	#9
eepiccolo Dec 2002 Frederick County, MD 2×5×37 Posts	My computer at home uses the on-board video on the M-board. I'll have to fiddle around with it and see what happens.

2003-06-24, 04:46	#10
hyh1048576 Jun 2003 2⁶ Posts	Hmm,here is my result: colour 24bit 16bit 8bit(256 colour) resolution 640480 0.294 0.286 0.278 800600 0.304 0.296 0.283 1024768 0.328 0.307 0.291 1152864 0.345 0.321 0.292 12801024 0.382 0.344 0.301 16001200 /////// /////// 0.319 ******************************************** From 0.382 to 0.278,it can be 37% faster! MY GOD!I hope I have a 2-colour screen!....... PS:Can the resolution be 12801024? I think it should be 1280960,for the resolution is always 4k*3k,here k is integer.But the screen said so.

2003-06-24, 05:22	#11
delta_t Nov 2002 Anchorage, AK 545₈ Posts	can you give us details of your computer?