@ wr104
Can you tell me how I can find out to determine my threads per core? I tried to google but can't find the correct answer.
I might have got lucky on my 280x. It is up and running at 135 kh/s and finding blocks decently but I can't get my 270x going. I keep getting HW errors. From what I can determine I have 1280 shaders on the 270x.
The two most important parameters for the cgminer-khc are the 'shaders' and the 'shaders_mul'. The former is straightforward. If you GPU has 2048 Stream Processors then, you need to use '--shaders 2048'. The latter is a bit more complicated to as it depends on the GPU architecture and how much memory you have in your video card. Unfortunately, the best value for 'shaders_mul' must be found through trial and error.
That said, with all the video cards that I tested, I found that the best value for 'shaders_mul' was always 8. But, your mileage may vary, if you know what I'm saying.
When I developed the kshake320 opencl kernel and I was testing it using CodeXL, I did find somewhere a good explanation on how to best determine the number of threads per Stream Processor. I'll try to find it.