Yes I know but I really love to see what happens when varying the parameters, I was surprised that with odd multiples of 32 for the worksize the hashrate dropped for example
It's not really for the sake of getting more out of the cards, as it is for curiosity
The native hardware worksize (AMD calls these wavefronts) on Radeon 5xxx is 64. Anything less than 64, or anything that isn't a multiple of 64, will run very badly (as half the pipes aren't running anything half or all the time). AMD recommends power of two (subtly implying 192 isn't worth it either).
The OpenCL spec also recommends a power of two and it also implies that implementations should rotate around multiples of 64.
Apparently, one can get 68.31 Mhash/s out of an Nvidia GTX460. I'm running about 20 Mhash/s less. Do I just have to mess with the -f and -w modifiers to improve my hash rate or is there any logic or known parameters I can use?
I'm not sure what a correct value is. Some Nvidia hardware has a minimum worksize of 32 (due to it's CUDA legacy where 32 was acceptable), some seem to have one of 64. Nvidia hardware isn't nearly as parallel as AMD hardware (its 16 wide SIMD in 16 independent pipes and requires 2 batches to pipeline effectively; Radeon 5xxx is 64 wide SIMD in 4+1 units of 4 plus ALU instruction batching), so -w may not have as much power as it does on AMD hardware.
So, try a bunch of values and see what they do. Worst case is 64 runs just as well as 256 or 512 does.
Also, as I said earlier in this thread, higher -f values increase desktop interactivity but effectively slow hashing. -f 1 maxes out performance but makes your desktop useless. Nvidia drivers are badly designed enough that you could lose 20 mhash by not running at low -f values.
