Prime95 version 27.7 / 27.9 - Page 22

James Heinrich · 2013-06-06, 01:32

This I guess falls under user-error / GIGO, but Prime95 will crash on a PRP test that specifies all the factors for a fully-factored exponent (leaving nothing left to check for probable-primality). For example:

Code:

PRP=1,2,101,-1,"7432339208719,341117531003194129"

ramgeis · 2013-06-13, 22:42

I'm testing v27.9 build 1 on a dual e5-2670 xeon system (16 physical cores, 32 with hyperthreading, everything detected correctly) and there seems to be a problem with the expected completion date calculation. I did LL tests on all 32 cores and the estimated completion time was always approximately twice as long compared to reality (no restriction in the settings).

kladner · 2013-06-13, 22:48

The general wisdom is that hyperthreads do not help, and may even hurt performance in Prime 95. The only circumstance, IIRC, in which it seems to be a benefit is when other uses (software) are competing for CPU time.

kladner · 2013-06-14, 04:30

Quote:

Originally Posted by kladner

The general wisdom is that hyperthreads do not help, and may even hurt performance in Prime 95. The only circumstance, IIRC, in which it seems to be a benefit is when other uses (software) are competing for CPU time.

To be a bit more precise, an LL worker in Prime 95 will completely occupy a physical core. There is no gain in running more workers than you have physical cores. Even with hyperthreading enabled, you need to arrange Prime 95 to run only on "real", not virtual cores.

Search the forum for "affinity scramble". Note that it is far more effective to search via Google with "site: mersenneforum.org [search terms]" (no quotes, no brackets.)

ramgeis · 2013-06-14, 15:40

It's always good to check the general wisdom from time to time to see if it's still valid. ;)

Since the first CPUs with hyperthreading came out I always tried to find the best work scenario for Prime95 for a given system. If I remember correctly back then the best combination on the first single core CPU with hyperthreading was to do a LL-Test on one virtual core and a TF-Test on the other.

On the system mentioned in my original message running Prime95 on all 32 virtual cores is approx. 15% faster than running only on 16 physical cores.

Anyway, my observation regarding the faulty expected completion date calculation is independent from the number of used CPU cores. On that system it seems to always differ by a factor of ~2.

Uncwilly · 2013-06-15, 02:32

Is there a way to keep Prime95 from sending back to PrimeNet every time I adjust memory settings? I change the memory setting on my machines if I know that I will be away from them for a while. I set the day time memory to be the same as nighttime. I would prefer it if I could shut off the check-in.

Prime95 · 2013-06-15, 12:04

Quote:

Originally Posted by Uncwilly

I would prefer it if I could shut off the check-in.

Options / Manual Communication

dbaugh · 2013-06-16, 07:32

I understand what FFT2=2480K does but, what does FFT2=3M mean?

firejuggler · 2013-06-16, 09:52

kilo, mega, tera?
FFT2=3M is FFT2=3072K

LaurV · 2013-06-17, 07:42

Still waiting to see the time when my personal computer will be able to use a tera-FFT... Or at least few-giga-FFT... hehe.. I will go for the big EFF money...

pepi37 · 2013-07-16, 09:52

I use Prime 27.9 if I need quickly to verify that number is PRP or not. But I noticed next behavior, and that is in same time question: I can set program to use 4 threads on quadcore CPU, and it is ok, but Prime only uses about 72-80% of CPU. Can I manage to to get 100% of use?
This is local.txt

Quote:

OldCpuSpeed=3829
NewCpuSpeedCount=0
NewCpuSpeed=0
RollingAverage=1000
RollingAverageIsFromV27=1
ComputerGUID=xxxxxxxxxxxxxxx
WorkerThreads=1
Affinity=99
ThreadsPerTest=4
RollingHash=1257001510
RollingCompleteTime=104

2013-06-06, 01:32	#232
James Heinrich "James Heinrich" May 2004 ex-Northern Ontario 11·311 Posts	This I guess falls under user-error / GIGO, but Prime95 will crash on a PRP test that specifies all the factors for a fully-factored exponent (leaving nothing left to check for probable-primality). For example: Code: PRP=1,2,101,-1,"7432339208719,341117531003194129"

2013-06-13, 22:42	#233
ramgeis Apr 2013 3²·13 Posts	I'm testing v27.9 build 1 on a dual e5-2670 xeon system (16 physical cores, 32 with hyperthreading, everything detected correctly) and there seems to be a problem with the expected completion date calculation. I did LL tests on all 32 cores and the estimated completion time was always approximately twice as long compared to reality (no restriction in the settings). Last fiddled with by ramgeis on 2013-06-13 at 22:56

2013-06-13, 22:48	#234
kladner "Kieren" Jul 2011 In My Own Galaxy! 27AE₁₆ Posts	The general wisdom is that hyperthreads do not help, and may even hurt performance in Prime 95. The only circumstance, IIRC, in which it seems to be a benefit is when other uses (software) are competing for CPU time. Last fiddled with by kladner on 2013-06-13 at 22:48

2013-06-14, 15:40	#236
ramgeis Apr 2013 3²·13 Posts	It's always good to check the general wisdom from time to time to see if it's still valid. ;) Since the first CPUs with hyperthreading came out I always tried to find the best work scenario for Prime95 for a given system. If I remember correctly back then the best combination on the first single core CPU with hyperthreading was to do a LL-Test on one virtual core and a TF-Test on the other. On the system mentioned in my original message running Prime95 on all 32 virtual cores is approx. 15% faster than running only on 16 physical cores. Anyway, my observation regarding the faulty expected completion date calculation is independent from the number of used CPU cores. On that system it seems to always differ by a factor of ~2. Last fiddled with by ramgeis on 2013-06-14 at 15:41

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2013-06-15, 02:32	#237
Uncwilly 6809 > 6502 """"""""""""""""""" Aug 2003 101×103 Posts 2·4,909 Posts	Is there a way to keep Prime95 from sending back to PrimeNet every time I adjust memory settings? I change the memory setting on my machines if I know that I will be away from them for a while. I set the day time memory to be the same as nighttime. I would prefer it if I could shut off the check-in.

2013-06-16, 07:32	#239
dbaugh Aug 2005 2·59 Posts	I understand what FFT2=2480K does but, what does FFT2=3M mean?

2013-06-16, 09:52	#240
firejuggler Apr 2010 Over the rainbow 101000101110₂ Posts	kilo, mega, tera? FFT2=3M is FFT2=3072K

2013-06-17, 07:42	#241
LaurV Romulan Interpreter Jun 2011 Thailand 7²×197 Posts	Still waiting to see the time when my personal computer will be able to use a tera-FFT... Or at least few-giga-FFT... hehe.. I will go for the big EFF money...