cgminer settings [ ati / amd radeon HD6870 GPU ] scrypt I'm found that speed of my cgminer should be around 320kh/s:

https://litecoin.info/Mining_hardware_comparison

ati / amd radeon HD6870 GPU

The wiki recommend use this -I 19 -g 1 -w 256 --thread-concurrency 8192

However, I can not use -I more than 11, because hardware errors HW

My current success is ~ 150Kh/s: 

./cgminer --scrypt --gpu-platform 0 -T --no-submit-stale --queue 4 --scan-time 1 --intensity 11  --thread-concurrency 2048 --load-balance --url stratum+tcp://

(5s):141.5K (avg):141.3Kh/s | A:631234  R:0  HW:0  WU:118.9/m
(5s):153.7K (avg):147.4Kh/s | A:1261234  R:0  HW:0  WU:141.2/m


When I set --intensity more than 11, i'm always get a hardware error and no accepted shares:


12 - only errors - HW, no accepted shares:


(5s):145.5K (avg):145.0Kh/s | A:0  R:0  HW:12  WU:9.1/m

(5s):145.9K (avg):145.1Kh/s | A:0  R:0  HW:12  WU:8.2/m

(5s):147.0K (avg):145.4Kh/s | A:0  R:0  HW:13  WU:7.5/m

...


16 - speed growth, but no accepted shares, only HW :


(5s):179.4K (avg):279.3Kh/s | A:0  R:0  HW:39  WU:27.2/m

(5s):226.5K (avg):269.4Kh/s | A:0  R:0  HW:54  WU:13.7/m


18 - very huge desktop lag, no accepted shares, and HW growth very fast:


(5s):188.2K (avg):296.4Kh/s | A:0  R:0  HW:52  WU:0.0/m

(5s):230.4K (avg):295.9Kh/s | A:0  R:0  HW:82  WU:0.0/m

(5s):256.3K (avg):295.9Kh/s | A:0  R:0  HW:106  WU:0.0/m

(5s):271.9K (avg):295.8Kh/s | A:0  R:0  HW:126  WU:0.0/m


20 - good bye Desktop. HW


(5s):273.9K (avg):287.7Kh/s | A:0  R:0  HW:194  WU:1.3/m

(5s):285.6K (avg):289.4Kh/s | A:0  R:0  HW:224  WU:1.1/m

(5s):264.7K (avg):292.4Kh/s | A:0  R:0  HW:325  WU:1.6/m

This is around declared in Wiki 320ks/s, but it is not a workable state, there are only errors - HW.

However, there is another mistake in wiki: --thread-concurrency 8192, my card have no enough RAM:

 [2013-12-02 17:02:00] Maximum buffer memory device 0 supports says 134217728                    
 [2013-12-02 17:02:00] Your scrypt settings come to 13428326


This told me cgminer, when I make +1 to  --thread-concurrency 2049



What is the magical border between 11 and 12 intensity?

I do not touch default Core and Memory Clocks:

$ amdconfig  --odgc

Default Adapter - AMD Radeon HD 6800 Series 
                            Core (MHz)    Memory (MHz)
           Current Clocks :    300           300
             Current Peak :    915           1050
  Configurable Peak Range : [400-1100]     [500-1260]
                 GPU load :    8%


How can I achieve workable 320 kh/s, as wiki told?
Optimum hash rate depends not just on the parameters sent to cgminer but also on how was this program compiled, if it's 32bits/64bits, and the OS configuration.

The best results I've seen are with Gentoo Linux - as you may know, with this distro you first stablish your specific hardware configuration and then compile everything from code, thus optimizing all our software for the hardware you have to extract the most value off of it.

Something you do can do without going the esoteric route of OS tweaking, you could try modifying the GPU's mem clock as well as (slightly) overclocking. Usually, once you hit the point of diminishing returns with the intensity, thread-concurrency and work unit those are the next values to tweak.

If you haven't read the "README" file from Con Kolivas himself, when discussing Litecoin he delineates an optimizing algorithm in which you first find a sweat spot with intensity, then with another value, then another... finally going to mem clock and overclocking, he says you'll extract the best performance that way - such approach is valid for all scrypt-based coins.