L2 cache unknown with new CPUs

ahmerali · 2006-11-12, 23:15

On a lot of the newer machines I am using, especially Conroes, Prime95 is displaying L2 cache size: unknown under CPU properties. Clearly I'm not getting the benefit of these CPUs. Sometimes even the L1 cache is not detected properly. Any advice on settings for this?

Prime95 · 2006-11-13, 00:17

Look in undoc.txt for the local.ini setting that tells prime95 how much L2 cache is available.

ahmerali · 2006-11-13, 04:12

Thanks, that works for the L2 cache I suppose, even though the display in Prime95 still shows "unknown"...anything for the L1 cache, or is that not so important?

Prime95 · 2006-11-13, 04:38

L1 cache is irrelevant in FFT selection

Cruelty · 2006-11-13, 15:50

The question is how to set L2 cache in Prime95 on multi-core CPUs with L2 cache shared among several CPUs? Should I set "CpuL2CacheSize" variable to 50% of the total amount of L2 cache, for each copy of Prime95?

Prime95 · 2006-11-14, 01:20

I'd do 50%. It will likely choose the same FFT implementation for either size.

Longshot · 2006-11-29, 13:40

I have found that L2 cache and FSB speed add nothing to speeding up LL testing. My XP2800 Thoroughbred outperforms my XP3200 Barton. The Barton has a 400 Mhz FSB and the Thoroughbred has a 333 FSB. It seems to me that CPU clock speed and the various SSE instruction sets make the most difference.

Cruelty · 2006-11-30, 08:34

L2 cache size has (or at least should have) an impact on the performance while running LL test - it all depends on the length of FFT used.
Add "FullBench=1" to your prime.ini file and check the results

BTW: according to this document (page 42+43) your XP2800 has slight (50MHz) speed advantage over XP3200

Longshot · 2006-12-09, 19:08

OK. I put it in there and I will let you know how it turns out. Thanks for the tip.

2006-11-12, 23:15	#1
ahmerali Jul 2005 13₁₆ Posts	L2 cache unknown with new CPUs On a lot of the newer machines I am using, especially Conroes, Prime95 is displaying L2 cache size: unknown under CPU properties. Clearly I'm not getting the benefit of these CPUs. Sometimes even the L1 cache is not detected properly. Any advice on settings for this?

2006-11-29, 13:40	#7
Longshot Mar 2004 Somewhere downrange 16₈ Posts	L2 cache & FSB speed I have found that L2 cache and FSB speed add nothing to speeding up LL testing. My XP2800 Thoroughbred outperforms my XP3200 Barton. The Barton has a 400 Mhz FSB and the Thoroughbred has a 333 FSB. It seems to me that CPU clock speed and the various SSE instruction sets make the most difference.

2006-11-30, 08:34	#8
Cruelty May 2005 2³×7×29 Posts	L2 cache size has (or at least should have) an impact on the performance while running LL test - it all depends on the length of FFT used. Add "FullBench=1" to your prime.ini file and check the results BTW: according to this document (page 42+43) your XP2800 has slight (50MHz) speed advantage over XP3200 Last fiddled with by Cruelty on 2006-11-30 at 08:44

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2006-11-13, 00:17	#2
Prime95 P90 years forever! Aug 2002 Yeehaw, FL 2×53×71 Posts	Look in undoc.txt for the local.ini setting that tells prime95 how much L2 cache is available.

2006-11-13, 04:12	#3
ahmerali Jul 2005 19 Posts	Thanks, that works for the L2 cache I suppose, even though the display in Prime95 still shows "unknown"...anything for the L1 cache, or is that not so important?

2006-11-13, 04:38	#4
Prime95 P90 years forever! Aug 2002 Yeehaw, FL 2×53×71 Posts	L1 cache is irrelevant in FFT selection

2006-11-13, 15:50	#5
Cruelty May 2005 2³×7×29 Posts	The question is how to set L2 cache in Prime95 on multi-core CPUs with L2 cache shared among several CPUs? Should I set "CpuL2CacheSize" variable to 50% of the total amount of L2 cache, for each copy of Prime95?

2006-11-14, 01:20	#6
Prime95 P90 years forever! Aug 2002 Yeehaw, FL 2×53×71 Posts	I'd do 50%. It will likely choose the same FFT implementation for either size.

2006-12-09, 19:08	#9
Longshot Mar 2004 Somewhere downrange 14₁₀ Posts	OK. I put it in there and I will let you know how it turns out. Thanks for the tip.