Bitcoin Forum

Hi,

I added second screen to my radeon 6770. Previously my cgminer ran GPU 0 and thread 0, but now it runs GPU 1 and 2, and 2 threads. It tells at start up ADL found less devices than opencl. What setting I need to give to cgminer to ran like it ran with one screen?

Did the overall hash rate diminish?

Total hashrate is win-loose. If I use computer, hash rate is about 140M and fluctuates a lot, not surprise while two monitors, when I dont use machine, hash rate is up to 190M. With one screen it is pretty constant 180M, no matter if I use machine or not.

Seems like the second screen slows it down

The root cause of the change is that AMD drivers are composed of loosely connected sets of technologies:
ADL - used for clocks, voltage temperature and fan control - being hardware-bound, sees only one device.
OpenCL - the language used for GPGPU ops - sees one device per each connected VDU.
Unfortunately, no one has been able to reliably tie ADL devices to their corresponding OpenCL virtual devices or in some scenarios (some systems using multiple double-GPU cards) even to the correct physical device!

I'm not exactly sure this matter requires any action on your part but if you wand to do something about it, one of the virtual openCL devices can be disabled with disable-gpu.
The number of threads per GPU core can be specified with gpu-threads.
It's all pretty well documented in the HOWTO (https://github.com/ckolivas/cgminer/blob/master/README).

OpenCL sees every display-enabled device as a separate device. This means that 2 displays on one GPU comes up as 2 devices and there is no way for the software to tell a virtual device from a physical one. So your one physical device attached to two monitors will be mined as though they're two separate devices and the overall hashrate will be identical, half coming from each. Apart from disabling one of the devices on the command line with -d, there is no workaround for this amd fail short of unplugging the monitor.