Prime95 vs. CUDALucas

[storm5510]

This is in regard to the following assignment:

Test=A5992806202E1212029B4F9445CE945D,79437629,75,1

I was thinking Culu would run much faster than Prime95. In the attached image showing a comparison between the two running the same test. Culu runs only 13% faster than Prime95. Does anyone have any ideas as to why this is happening?

Edit: I am using an nVidia GTX-750Ti and CUDA 8.

[fivemack]

And what processor are you comparing it against?

Modern graphics cards do not have exceptionally good double-precision performance; a GTX1080 is 256 gigaflops peak, which is the same peak as a quad-core 4GHz Haswell. The GTX750Ti is about 40 gigaflops peak, so slower than a single core of a 4GHz Haswell.

[ATH]

The last Nvidia cards with "good" double precision performance was like GTX 580/590 and then the original Titan from 2013 and Titan Black / Titan Z from 2014 in the 700 series.

By "good" I mean 1/3rd of its single precision performance. All consumer cards since has DP performance of 1/24th or 1/32th of its SP performance.

http://www.mersenne.ca/cudalucas.php


Maybe you should use the SP performance for factoring with mfaktc instead.

Your 750Ti has 1306 GFLOPs SP and 40.8 GFLOPs DP:
https://en.wikipedia.org/wiki/GeForce_700_series

[storm5510]

Originally Posted by fivemack

And what processor are you comparing it against?

i5-3570 @ 3.4 GHz.

Originally Posted by ATH

Maybe you should use the SP performance for factoring with mfaktc instead.

Your 750Ti has 1306 GFLOPs SP and 40.8 GFLOPs DP:

So, you are saying there are two different ways to run Culu and mfaktc? I am not familiar with SP and DP. How do I do this?

[CRGreathouse]

Originally Posted by storm5510

So, you are saying there are two different ways to run Culu and mfaktc? I am not familiar with SP and DP. How do I do this?

SP is single-precision (32 bits), DP is double-precision (64 bits). Your GPU can do single-precision operations 32 times faster than it can do double-precision operations, so you'd be better off doing work that requires only single-precision. (If SP was, say, only 4 times faster than DP you'd be better off doing DP work.)

I think that ATH was suggesting that you use mfaktc instead of Culu, rather than switching modes of one or the other.

[ATH]

Yes, CUDALucas requires double precision, and it is therefore slow because it is running only 1/32 of your cards single precision performance.

It would probably be more beneficial for GIMPS and for the amount of GHz-days accumulating on your account (if you care about that) if you do factoring on the card with mfaktc (single precision) instead of LL tests with CUDALucas (double precision).

[storm5510]

Originally Posted by ATH

It would probably be more beneficial for GIMPS and for the amount of GHz-days accumulating on your account (if you care about that) if you do factoring on the card with mfaktc (single precision)...

This is primarily what I have been doing. I wanted to see how CUDALucas would perform on this hardware. Obviously, not as good as others. Case closed.