GPU Trial Factoring FAQ

[Redarm]

win 7 64bit

cudart64_41_28.dll
cudart64_40_17.dll

[Dubslow]

Hmm... yeah I have no clue. Could a mod move these to the mfaktc thread?
Edit: For further trouble shooters' sake, he does have up to date drivers (301.x).

[Bdot]

I just wanted to mention here that I moved mfakto to http://mersenneforum.org/mfakto, latest version now at
http://mersenneforum.org/mfakto/mfakto-0.11

So this should match mfaktc much better ...

[lorgix]

Does feeding two GPUs from a single physical (hyperthreaded) core work well?

[Bdot]

Originally Posted by lorgix

Does feeding two GPUs from a single physical (hyperthreaded) core work well?

Yes, you can use two hyper-threads (HT) of one core to run two mfaktc/o instances, each bound to a different GPU. In fact, you can even let the two instances share one HT and still use two different GPUs. It's all a question of how much CPU-power you want to invest. Using faster cards it is quite likely, that a shared HT will be insufficient to fully utilize the GPUs, even at minimal sieving.

[lorgix]

Originally Posted by Bdot

Yes, you can use two hyper-threads (HT) of one core to run two mfaktc/o instances, each bound to a different GPU. In fact, you can even let the two instances share one HT and still use two different GPUs. It's all a question of how much CPU-power you want to invest. Using faster cards it is quite likely, that a shared HT will be insufficient to fully utilize the GPUs, even at minimal sieving.

The cards would probably be pretty weak, in this case.

So it should be efficient? They don't stomp on each other?

How do I choose which instance uses what GPU? (I use mfaktc-0.18)

[Bdot]

Originally Posted by lorgix

The cards would probably be pretty weak, in this case.

So it should be efficient? They don't stomp on each other?

How do I choose which instance uses what GPU? (I use mfaktc-0.18)

The "stomping on each other" is no different than when using separate cores (apart from having less computing power). Well, as they would share the L1-cache, sieving is probably a bit slower than half of "single instance on a core". But if you have weak GPUs, this will not matter much.

Use -d <dev number> to specify the CUDA device (same numbering scheme - start from 0).

[lorgix]

Originally Posted by Bdot

The "stomping on each other" is no different than when using separate cores (apart from having less computing power). Well, as they would share the L1-cache, sieving is probably a bit slower than half of "single instance on a core". But if you have weak GPUs, this will not matter much.

Use -d <dev number> to specify the CUDA device (same numbering scheme - start from 0).

OK, I think half a core will be enough.

I'm sorry; I don't understand where that number is supposed to come from.

edit: Trial & error never fails.. oh wait..

[Dubslow]

Just count your GPUs from 0. The first would be "-d 0", the second would be "-d 1", etc... if the cards are different models just use trial and error to figure out which one is which.

[lorgix]

Originally Posted by Dubslow

Just count your GPUs from 0. The first would be "-d 0", the second would be "-d 1", etc... if the cards are different models just use trial and error to figure out which one is which.

Oh, it was that simple. Thanks.

[aketilander]

Originally Posted by Dubslow

Just count your GPUs from 0. The first would be "-d 0", the second would be "-d 1", etc... if the cards are different models just use trial and error to figure out which one is which.

Well I think if you have two cards of different brands, one AMD and one NVIDIA in the same computer both are counted as the first one, so the switch should be "-d 0" or rather you don't need the switch at all, that is you can run mfakto and mfaktc without a switch, or if you like to use the switch it should be "-d 0" in both programs. The switch is only needed if you have more then one card of the same brand.

Well, I may be wrong on this one.