Mfaktc sieveprimes=5000 OK?

NBtarheel_33 · 2011-10-07, 19:37

Hi,

I'm playing with the GPU and mfaktc again, and I've noticed that if I adjust SievePrimes down from the default 25000 to 5000, I get a significant speedup. Is there any downside to reducing SievePrimes? Can this cause factors to be missed?

TheJudger · 2011-10-07, 20:01

Hi,

Quote:

Originally Posted by NBtarheel_33

I'm playing with the GPU and mfaktc again, and I've noticed that if I adjust SievePrimes down from the default 25000 to 5000, I get a significant speedup. Is there any downside to reducing SievePrimes? Can this cause factors to be missed?

Unless there is an undiscovered bug the value of SievePrimes does not cause missing factors.
Significant speedup... how much faster is it? Keep in mind that the avg. rate doesn't really matters. What matters is the time per class/assignment.

Perhaps you want to dedicate another core to mfaktc. SievePrimes=5000 usually tells you that not enough CPU resources are available. Just start another copy of mfaktc in a separate directory working on different exponents.

Oliver

Dubslow · 2011-10-08, 00:43

What is avg. rate then if it doesn't really matter? I notice the same thing, where the speed up is in avg. rate. (the auto adjust doesn't up it from 5000 if that matters)

Christenson · 2011-10-08, 03:02

Oliver, correct me if I'm wrong, but I think that Average Rate refers to the rate at which the GPU takes candidate factors (output from the prime sieve running on the CPU, which at sieveprimes = 5,000, is doing a relatively worse job of eliminating things that can't be factors) and determines whether the candidates are or are not factors.

Classes, on the other hand, represent a fixed division in the population of all possible factors, so you want those to fly by as fast as possible.

A low sievePrimes indicates that the CPU core is saturated, and you *may* want to add another CPU to the job by running a second copy of mfaktc on a different core. (But possibly not, as this other core could be doing P-1 or LL tests)

Chuck · 2011-10-09, 00:59

Mfaktc on my system always adjusts sieveprimes down to 5000 after a few seconds of operation. I tried shutting off the automatic adjustment and using higher values, but 5000 always gives me the best performance (least amount of total time spent).

I am running two instances of mfaktc, two LL tests, one DC and one P-1 on a six-core system (core-i7, hyperthreading off).

Chuck

Christenson · 2011-10-09, 20:12

Quote:

Originally Posted by Chuck

Mfaktc on my system always adjusts sieveprimes down to 5000 after a few seconds of operation. I tried shutting off the automatic adjustment and using higher values, but 5000 always gives me the best performance (least amount of total time spent).

I am running two instances of mfaktc, two LL tests, one DC and one P-1 on a six-core system (core-i7, hyperthreading off).

Chuck

Assuming you have set up the instances of mfaktc to run on two separate cores using your operating system, that means you have a very nice GPU that your CPU isn't quite keeping up with, so the low sieveprimes reduces the CPU load per class, and makes the GPU, with the spare cycles available, do a little more work.

Chuck · 2011-10-09, 21:41

Quote:

Originally Posted by Christenson

Assuming you have set up the instances of mfaktc to run on two separate cores using your operating system, that means you have a very nice GPU that your CPU isn't quite keeping up with, so the low sieveprimes reduces the CPU load per class, and makes the GPU, with the spare cycles available, do a little more work.

It is a GTX580 Black Ops (797 MHz default clock)

Chuck

Christenson · 2011-10-09, 22:10

Quote:

Originally Posted by Chuck

It is a GTX580 Black Ops (797 MHz default clock)

Chuck

QED, a *very* nice GPU!

Dubslow · 2011-10-10, 02:25

Quote:

Originally Posted by Chuck

It is a GTX580 Black Ops (797 MHz default clock)

Chuck

daaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaannnnnnnnnnnnnnnnnnnnnnnngggggggggggggg

kjaget · 2011-10-10, 16:57

Quote:

Originally Posted by Chuck

Mfaktc on my system always adjusts sieveprimes down to 5000 after a few seconds of operation. I tried shutting off the automatic adjustment and using higher values, but 5000 always gives me the best performance (least amount of total time spent).

This might be telling you that there's a benefit to running a 3rd instance of mfaktc to keep the card fed with data?

Chuck · 2011-10-10, 17:11

Quote:

Originally Posted by kjaget

This might be telling you that there's a benefit to running a 3rd instance of mfaktc to keep the card fed with data?

No, it's running at 85% GPU load.

Chuck

2011-10-07, 19:37	#1
NBtarheel_33 "Nathan" Jul 2008 Maryland, USA 5×223 Posts	Mfaktc sieveprimes=5000 OK? Hi, I'm playing with the GPU and mfaktc again, and I've noticed that if I adjust SievePrimes down from the default 25000 to 5000, I get a significant speedup. Is there any downside to reducing SievePrimes? Can this cause factors to be missed?

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2011-10-08, 00:43	#3
Dubslow Basketry That Evening! "Bunslow the Bold" Jun 2011 40<A<43 -89<O<-88 3×29×83 Posts	What is avg. rate then if it doesn't really matter? I notice the same thing, where the speed up is in avg. rate. (the auto adjust doesn't up it from 5000 if that matters)

2011-10-08, 03:02	#4
Christenson Dec 2010 Monticello 5·359 Posts	Oliver, correct me if I'm wrong, but I think that Average Rate refers to the rate at which the GPU takes candidate factors (output from the prime sieve running on the CPU, which at sieveprimes = 5,000, is doing a relatively worse job of eliminating things that can't be factors) and determines whether the candidates are or are not factors. Classes, on the other hand, represent a fixed division in the population of all possible factors, so you want those to fly by as fast as possible. A low sievePrimes indicates that the CPU core is saturated, and you may want to add another CPU to the job by running a second copy of mfaktc on a different core. (But possibly not, as this other core could be doing P-1 or LL tests)

2011-10-09, 00:59	#5
Chuck May 2011 Orange Park, FL 885₁₀ Posts	Mfaktc on my system always adjusts sieveprimes down to 5000 after a few seconds of operation. I tried shutting off the automatic adjustment and using higher values, but 5000 always gives me the best performance (least amount of total time spent). I am running two instances of mfaktc, two LL tests, one DC and one P-1 on a six-core system (core-i7, hyperthreading off). Chuck