Hi all! I have a question regarding CUDA 2.1 and GTX295. I see that CUDA presents GTX 295 as 2 separate devices. Is it possible to use them as single device? Thank you!
Short answer: no.
Longer answer: 295 is physically two cards. Games can see it as a single rendering device thanks to built in SLI, but the way SLI automagically splits load between two cards is not applicable to GPGPU (it basically splits the screen in half and sends each card one part) so it has to be turned off and task splitting has to be made explicitly by the programmer.
Big_Mac, thank you. It’s a sad news. I mean, it’s not a good idea to rewrite a codes for two separate GTX 260 devices :(
Actually it is, because then you can probably run it on even more devices after ;)
actually it alternates frames between the two devices; standard split frame rendering went away with 3dfx.
So using GTX 295 you see 2 devices from CUDA end you can select them with cudaSetDevice?
Is it that way?
cudaSetDevice() will let you decide what card you want to run the program on. There is a sample of code on http://forums.nvidia.com/index.php?showtopic=88503 which we wrote an algorithm to divide the job up between 4 cards (2xGTX295) in a single case.
But what about memory?
I’m going to buy this card, so can someone tell me, is the memory devided for two equal blocks or
each 260 core can access all memory?
For example, Zotac ZT-295E3MA-FSP declares 1792M of memory, can I access all of them in one cuda kernel?
No, it’s entirely two separate cards connected through a PCI-Express switch to the slot on the motherboard. Each circuit board on the GTX 295 has half of the streaming processors and half of the memory. In fact, each half of a GTX 295 looks to be exactly like an underclocked GTX 275.
Thank you very much, Seibert, you save my money ;)
While you are so kind, what is the difference between GTX275 and GTX280?
Maybe I’m unlucky, but I can’t find feature table in this site.
The quantity of MPs looks like the same - 30…
The GTX 275 has a smaller memory bus (448 bits instead of 512), and correspondingly less memory (898 MB instead of 1024 MB). The GTX 275 is clocked higher than the GTX 280, but less than the GTX 285.
This is a handy page for comparing the different GPUs: