Archives Discussions

[honzas7]

Hi there,

my primary GPU is nVidia (GS7100) and now I would like to do computations using OpenCL with ATI HD5770 (plugged in as secondary GPU). Is it possible to use OpenCL in this configuration?

Thanks for response

[nou]

there is possibility. http://forums.amd.com/devforum/messageview.cfm?catid=328&threadid=117913

[honzas7]

Thanks for the link. However, I've forgotten to point out, that the OS is Windows XP (SP3).

[empty_knapsack]

It's pretty much impossible to use ATI GPU as secondary one under Windows. It requires video driver to be loaded and Windows "doesn't like" 2 different video drivers working at the same time.

However it's possible to use ATI GPU as primary GPU and nVidia GPU as secondary being activated as PhysX device (some tweaks needed though and nVidia GPU must be G80+ ofc).

[nou]

as i know that only Vista refuse work with two different video drivers. in windows Xp and 7 it is possible to work.

[empty_knapsack]

Still there are more problems with ATI windows drivers than with nVidia ones. For example, it's possible to use all nVidia GPU devices under Windows XP without attaching monitors to each of them. For ATI GPUs it isn't true -- if there no monitor (or dummy plug) attached driver simply refuse to recognize GPU device at all. It's pretty annoying tbh.

 Also there is (was? not sure it was fixed especially for Windows) problem with recognizing more than 4 ATI GPUs at system. For nVidia it's OK to use 8 devices (actually recently guys at http://fastra2.ua.ac.be/ got 13(!) GPUs working within single system).

And this is ATI driver level issue, so while Windows itself can supports more than 4 GPU devices, ATI drivers can't.

[nou]

more than 4 GPU is seemd possible now http://forums.amd.com/devforum/messageview.cfm?catid=328&threadid=122135&enterthread=y

[empty_knapsack]

Yeah, I've seen that topic. But it's still unclear will such system normally works, not just detects > 4 GPUs.

Looks like zpdixon wasn't able to resolve "one of the 5 GPUs runs more slowly than the others" issue.

Also note that it was done with Linux not Windows (as well as 13x nVidia GPUs system also requires Linux).

[pupkin2000]

I use NV GTX280 and ATI HD5870 in same machine under Win7/x64.

I've two displays, one attached to NVidia, another to ATI.

In general, there is no problems with OpenCL:

 The NV's OpenCL.DLL is in Windows\SysWOW64 folder

 The ATI one in \Program Files\ATI Stream

So, I can switch GPU used simply by changing PATH in enviroment.

Many NVidia and\or ATI samples are working without recompilation, just by OpenCL.dll replacement. Some samples not working because feature set is different (for example. NVidia's oclNbody sample cannot draw in window because of lack of OpenGL/OpenCL integration in ATI OpenCL implementation).

I was unable to use HD5870 without display attached, but have not dig this problem in depth.