Dual CPU perfomance hit - Page 3

BigRed · 2002-10-10, 17:03

garo said:
If you are interested in finding a prime go with 2 LL test on each of the P4 duallies.

Yeah, if I'm interested in finding a prime then the best thing to do is nothing but regular LL tests. Let's assume I know my chances of finding a prime are minimal and I'm motivated by my stats. I've got 25 machines and I'm showing over 10000 P90 CPU hrs/day. Is the PC-800 RAMBus fast enough to minimize memory contention with 2 LL tests going on?
Factoring on the P4s would be good to make best use of all their RAM?

ET_ · 2002-10-10, 17:10

Quote:

Originally Posted by BigRed

Factoring on the P4s would be good to make best use of all their RAM?

AFAIK Factoring is more RAM consuming than LL tests...

Luigi

garo · 2002-10-11, 02:14

No Trial Factoring usually works in 8MB or so.

Primenet keeps two kinds of stats LL test CPU years and Factoring CPU years. Depends which one you want to ace at. If you run two LL test in parallel your output would be about 150% of what it would be if you ran only one test. If you run 2 factoring tests in parallel your output would be 200% but in factoring. If you ran one factor and one LL test you would get 100% in factoring and 100% in LL tests. So the choice is yours.

xtreme2k · 2002-10-11, 06:13

The thing is that would you rather get 150% cpu times recorded at primenet or would you rather to have 110% recorded?

Remember factoring only accounts for 10% of the ACTUAL time used.

Also I believe when you have faster memories, bigger caches, the 150% figure will increase substantially. From my understanding, the original recommendation of running 1LL + 1Fact is based on the Pentium 1 times where memory bandwidth was very low. Now that we have PC1066 or PC3200 I suspect we can give 2LL another try.

binarydigits · 2002-10-11, 07:27

Quote:

Originally Posted by xtreme2k

Remember factoring only accounts for 10% of the ACTUAL time used.

I keep seeing this 10% figured mentioned, and I would like to know from where it comes, since it is incorrect. It's more like 70%.

garo · 2002-10-11, 08:52

Yes the 10% figure is incorrect. The actual figure is closer to 100% but varies depending on whether you were lucky enough to find a factor.

The 10% figure comes from George's comment that one should spend 10% of one's CPU time factoring. That was the project ideal as he had envisaged.

xtreme2k · 2002-10-11, 10:53

It isnt incorrect.

Factoring is only WORTH 10% of the time used in P90 years. That is, if factoring a number took your computer 1 P90 year, only 0.1 P90 year will be credited. Thats where the 10% comes from.

xtreme2k · 2002-10-11, 10:57

Quote:

Why is factoring CPU time not ranked with equal weight as primality (Lucas-Lehmer) test CPU time?

Primality test time is purposefully biased. Here is the rationale behind the the ranking system used on the Top Producer Awards page:

We all know GIMPS finds Mersenne primes by systematic elimination of non-prime Mersenne numbers. A LL test returns a not-prime/prime result, but factoring can only at best produce a not-prime result. One might then say finding a factor eliminates a Mersenne candidate, so its CPU time should be weighted the same as a not-prime LL test's CPU time.

Yet in practice, the amount of CPU time attributed to having found factors is a small fraction of the total factoring effort. (I think this is because by the time exponents get into the PrimeNet database, all the easy factors have been found.) It is such a small fraction I just lump it together with the trial-factoring CPU time, which does not result in a not-prime/prime result.

Even if people choose factoring or primality test work, the ranking encourages a pattern of applied CPU time that is like a air-fuel combustion mixture, about a 10:1 ratio of LL CPU time to factoring CPU time.

I needed a way to balance the zoom-ahead factoring so those machines don't run out of things to do, which is easy to do until stronger factoring programs are available. The best way to do that is not to reward the time spent on it as much as the necessary but slow LL tests.

I think most people who start out factoring zoom ahead for a while, notice they only get partway up the list, then switch many of their machines to LL tests. It seems to work out as planned, but it's too soon to know how well it will continue. At the moment, I do not plan to change the ranking system from favoring primality tests.

Taken from http://mersenne.org/ips/faq.html

Hades_au · 2002-10-11, 13:02

Quote:

Originally Posted by BigRed

Let's assume I know my chances of finding a prime are minimal and I'm motivated by my stats

Well, if you are only motivated by stats, the way to maximise the production from your P4's is to do Double Checks. Double Checks will give the maximum return in P90 years.

Xyzzy, could I please have a different avatar, something from the Simpsons would be great :D

lycorn · 2002-10-11, 13:46

BigRed
As you are motivated by the stats, but also willing to find a new Mersenne Prime, I think that definitely the best move is to choose but First-time primality tests, and keep away from the 33M exponents. This way every new test stands some chances of finding a prime, and you´ll be moving faster up the charts, which is more motivating. You have fast enough machines for LL testing, leave the TF work for slower ones.

Xyzzy · 2002-10-11, 16:37

Quote:

Originally Posted by Hades_au

Xyzzy, could I please have a different avatar, something from the Simpsons would be great :D

Is Barney okay?

:D

2002-10-10, 17:03	#23
BigRed Oct 2002 11 Posts	Re: Best mix for dual P4 garo said: If you are interested in finding a prime go with 2 LL test on each of the P4 duallies. Yeah, if I'm interested in finding a prime then the best thing to do is nothing but regular LL tests. Let's assume I know my chances of finding a prime are minimal and I'm motivated by my stats. I've got 25 machines and I'm showing over 10000 P90 CPU hrs/day. Is the PC-800 RAMBus fast enough to minimize memory contention with 2 LL tests going on? Factoring on the P4s would be good to make best use of all their RAM?

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2002-10-11, 02:14	#25
garo Aug 2002 Termonfeckin, IE 101011010000₂ Posts	No Trial Factoring usually works in 8MB or so. Primenet keeps two kinds of stats LL test CPU years and Factoring CPU years. Depends which one you want to ace at. If you run two LL test in parallel your output would be about 150% of what it would be if you ran only one test. If you run 2 factoring tests in parallel your output would be 200% but in factoring. If you ran one factor and one LL test you would get 100% in factoring and 100% in LL tests. So the choice is yours.

2002-10-11, 06:13	#26
xtreme2k Aug 2002 2×3×29 Posts	The thing is that would you rather get 150% cpu times recorded at primenet or would you rather to have 110% recorded? Remember factoring only accounts for 10% of the ACTUAL time used. Also I believe when you have faster memories, bigger caches, the 150% figure will increase substantially. From my understanding, the original recommendation of running 1LL + 1Fact is based on the Pentium 1 times where memory bandwidth was very low. Now that we have PC1066 or PC3200 I suspect we can give 2LL another try.

2002-10-11, 08:52	#28
garo Aug 2002 Termonfeckin, IE 101011010000₂ Posts	Yes the 10% figure is incorrect. The actual figure is closer to 100% but varies depending on whether you were lucky enough to find a factor. The 10% figure comes from George's comment that one should spend 10% of one's CPU time factoring. That was the project ideal as he had envisaged.

2002-10-11, 10:53	#29
xtreme2k Aug 2002 2·3·29 Posts	It isnt incorrect. Factoring is only WORTH 10% of the time used in P90 years. That is, if factoring a number took your computer 1 P90 year, only 0.1 P90 year will be credited. Thats where the 10% comes from.

2002-10-11, 13:46	#32
lycorn "GIMFS" Sep 2002 Oeiras, Portugal 11000101110₂ Posts	BigRed As you are motivated by the stats, but also willing to find a new Mersenne Prime, I think that definitely the best move is to choose but First-time primality tests, and keep away from the 33M exponents. This way every new test stands some chances of finding a prime, and you´ll be moving faster up the charts, which is more motivating. You have fast enough machines for LL testing, leave the TF work for slower ones.