mfakto: an OpenCL program for Mersenne prefactoring

[Dubslow]

Feel free to continue work, but be aware that at some point in the future (admittedly probably not for at least a year, but I'm not the authority on this) that mfakt* will be integrated into Prime95. At such point, having its own GUI would probably be rendered redundant. If you still want to forge ahead though, go for it.

[flashjh]

Is there any way to reserve the 30M exponents that need DC TF 69 to 70?

[chalsall]

Originally Posted by flashjh

Is there any way to reserve the 30M exponents that need DC TF 69 to 70?

I'm being presumpious and am assuming you're talking to me wrt G72...

If you set the Pledge Level to 70, you will first be assigned candidates which have already been TFed to 69. There are (at this moment) 22 of them.

This is just a quick hack to facilitiate this -- I'll need to add the same Options feature as is available on the LLTF assignment page. Oh, and just to be pedantic, everything above 29.69M is to be taken to 70.

[flashjh]

Originally Posted by chalsall

I'm being presumpious and am assuming you're talking to me wrt G72...

Yes

If you set the Pledge Level to 70, you will first be assigned candidates which have already been TFed to 69. There are (at this moment) 22 of them.

Thanks!

[DigiK-oz]

Originally Posted by Dubslow

Feel free to continue work, but be aware that at some point in the future (admittedly probably not for at least a year, but I'm not the authority on this) that mfakt* will be integrated into Prime95. At such point, having its own GUI would probably be rendered redundant. If you still want to forge ahead though, go for it.

Thanks for the info. I hope mfakt* will soon be integrated into prime95. Till that happens, I want to get rid of the good old command prompt windows cluttering my taskbar :) It is a rather small programming effort (it is already working OK for single-GPU-brand systems). Of course, as soon as mfakt* is integrated I will ditch it :)

[Dubslow]

Well, okay. Like I said, it's likely to be a year or more, though I'm still not the authority on this. mfakt* are still, compared to Prime95, somewhat immature. (No wonder, since P95's been in development for ~15 years.)

[KyleAskine]

Does anyone have any idea on how the 79xx's should preform? I have a $50 giftcard to Newegg that expires at the end of the month, and am considering picking one up.

But with the absolute disaster that Cayman is in terms of TF (25% slower than Cypress), I wonder if Tahiti will be just as bad.

Edit - I am not looking for theoretical flops, since they do not tell the story with Cayman.

[Bdot]

Originally Posted by KyleAskine

Does anyone have any idea on how the 79xx's should preform? I have a $50 giftcard to Newegg that expires at the end of the month, and am considering picking one up.

But with the absolute disaster that Cayman is in terms of TF (25% slower than Cypress), I wonder if Tahiti will be just as bad.

Edit - I am not looking for theoretical flops, since they do not tell the story with Cayman.

That is really hard to tell until someone can try. Cayman's big issue is with 32-bit multiplications, which occupy 4 compute units (SIMDs) for one cycle. Some sources say that 3 compute units are used for that, but looking at the assembly I saw all 4 units busy with the same multiplication. Cypress, on the other hand, can also run only one 32-bit mul per cycle and SIMD-array. But there, only the "special" SIMD is occupied, the 4 simple ones can do other tasks.

mfakto's kernels (so far) have enough mul32 instructions that Cayman pays a lot of penalties for them. But there are also lots of other instructions that Cypress can run in parallel to the mul32 while Cayman needs to schedule them after mul32.

In the profiler I saw that the 800 SIMDs of a 5770 are utilized ~93% (when using proper vectoring). Only 7% of the cycles a SIMD will be unused because of instruction dependencies. This will be similar with the 1600 SIMDs of a 5870.

The 1536 SIMDs of a 6970 should be occupied almost 100% of the time with a vector size of 4 as they are independent. The poor mul32 is what hurts.

Back to the question: How fast will 7970 be? I expect it will also use 4 of its SIMDs for a mul32, therefore my assumption (which is kind of worst case) is, that the mfakto throughput will scale with the GFlops in comparison with Cayman. That is 2048 vs. 1536 SIMDs, and 925 vs. 880 MHz yielding 1.4 times the 6970 results.

If someone has access to one of these, I'd could provide an instrumented mfakto version telling exact kernel runtime numbers.

[KyleAskine]

I might buy a 7750 one they become available on Newegg, since I have a $50 gift card I need to use this month. If I do, I will try out mfakto once I get it!

[chair]

hello, I'm having trouble running 2 instances of mfakto. i have two graphics cards that meet the specs, but my trouble is where to enter the -d 2 (at least i think its that command) to tell the 2nd mfakto on what card to run.
id say that im new to this kind of computing, but i think this post already does. any help would be nice.

[Bdot]

Originally Posted by chair

hello, I'm having trouble running 2 instances of mfakto. i have two graphics cards that meet the specs, but my trouble is where to enter the -d 2 (at least i think its that command) to tell the 2nd mfakto on what card to run.
id say that im new to this kind of computing, but i think this post already does. any help would be nice.

Having -d 2 as the first option is usually good, but actually it should not matter where to place it (except for some test-modes), for example:

mfakto -d 2 -i instance2.ini

will try to use GPU #2 and read instance2.ini instead of mfakto.ini for the config parameters.

However, OpenCL also has the notion of "platforms", not just a simple numbering of all available GPUs. "Platforms" can be simplified as "vendors". Therefore, if you maybe have other OpenCL-enabled devices (built-in graphics, other GPUs), you may have to use the correct platform number. It's hard to predict in which order the platforms will appear. The clinfo tool can help to find out, but you need to install AMD APP SDK to use it. Or, you just try it out:

mfakto -d 11
mfakto -d 21
mfakto -d 31
...

This will use the first device of platform 1, 2, 3, ... Once you got the right platform that uses one of the GPU's you wish to use, then you can increase the last digit to use other devices of the same platform:

mfakto -d 22
mfakto -d 23
...