OpenCL platform vs device extensions

[imyxh]

cbang/src/cbang/hw/OpenCLLibrary.cpp

Lines 260 to 268 in 393020a

	// UUID
	if (exts.find("cl_khr_device_uuid") != exts.end())
	getKHRDeviceUUID(device, cd);
	// PCI Info
	if (exts.find("cl_khr_pci_bus_info") != exts.end())
	getKHRPCIBusInfo(device, cd);
	else TRY_CATCH_DEBUG(3, getPCIInfo(device, cd));

This seems to check that the OpenCL platform supports cl_khr_device_uuid and cl_khr_pci_bus_info. From what I have seen the notion of a platform extension is not extremely clear, and is probably not what we want to check for.

This issue blocks support for rusticl in fah-client (see FoldingAtHome/fah-client-bastet#239).

[jcoffland]

I don't see anything wrong with this code. This is inline with how the OpenCL API is defined. There's no ambiguity other than that some drivers may be buggy and not implement it correctly.

Does your driver cause an exception in these calls? If so I'd need to see the logs from that. All I've seen is that you commented some of this code out and your GPU started working. The reason it might work without PCI info is because fah-client guesses which GPU it's talking to which is easy if there's only one GPU. The only reason I could see your GPU failing with the above code is if it claimed to support one of those extensions but then returned an error when the extension was actually queried. But I'm just guessing.

[karolherbst]

You can't rely on the platform extensions containing all supported device extensions as it's the intersection of device extensions, not an union.

So the platform must not advertise cl_khr_device_uuid if a single device doesn't advertise it either.

Granted, the opencl impl in question here doesn't build the intersection at runtime, so extensions might not be listed as platform extensions on top, but applications can't rely on them anyway. Please use CL_DEVICE_EXTENSIONS or better CL_DEVICE_EXTENSIONS_WITH_VERSION instead.

[jcoffland]

I see, we need to be querying the device specific extensions rather than the platform extensions.