Intensity: How hard the miner is working. Each increase by one is DOUBLE the previous number of threads:
I:13 = 8192 threads
I:14 = 16384 threads
I:15 = 32768 threads
I:16 = 65536 threads
I:17 = 131072 threads
I:18 = 262144 threads
I:19 = 524288 threads
I:20 = 1048576 threads
As you can see this makes a major impact from level to level. You can use a comparison chart (Wiki) for all settings to get a good starting point for your gpu. If your feeling more crafty you can use xintensity.
Also with the new miners intensity limit has been increased up to 25. If your using a 290/290x you may want to go beyond the normal spectrum of 20 to see what happens thumb.gif (thanks for the reminder bargulator smile.gif)
xIntensity: Very new and still experimental and as far as I know only available from the kalroth release (see below). Seems to work flawlessly so far and gives a much more wide range of intensity. You can only use xintensity OR intensity NOT both. Calculated instead by the number of shaders your gpu has and multiplied by xintensity (Shaders*xI). So for example my 7870 and 270x have 1280 shaders, so any number I put in as the xintensity would be multiplied by 1280. both 80 (102400 which if you view above is equal to 16.7ish) and 111 (142080=17.25ish) seem to work really well on single thread I am not decided yet which is best will take some testing still biggrin.gif. Due to this I have also been able to get 2 threads to work which was not possible in the past. Its actually more productive and less system intensive to run 2 threads. I managed to get mine to run at xintensity=4 gpu-threads=2. This was NOT possible using normal intensity increases, Thanks kalroth!
Gpu-Threads: Now with the release of xintensity more cards will be able to hash at 2 threads and lower intensity. The reason you want this is less rejects. It may not work on all cards but its worth a shot. Alot of 280x/290x have no problem running 2 threads at a good hashrate (as they generally run at i-12 or i-13 with 2 threads anyways). My 7870 had to run on 1 thread to get the most performance. You will likely always end up on 1 or 2 threads.
Thread-Concurrency: This will be a tough one to tweak aswell. Best results are generally shaders*n+1. So for example my 7870 has 1280 shaders and i ended up personally thinking the best results came from 1280*8+1=10241 and also from 8193 which turns out seems to be a great number for MANY different cards using 2 threads. You will likely want to start with whats most common in the wiki.
Worksize: Can vary majorly from card to card. Alot of the tahiti and pitcairn cards use worksize 256. But you will still want to refer to the comparison chart (Wiki) to get the best starting point for your card. Then you will want to at least attempt multiple variations: 64,96,128,256 its possible any variation could see improvements. Most 7870 are at 128 or 256 while I personally got MUCH better results from 96. TRY EVERYTHING you never know what your card could do.
Device: Sets which gpu to use. I highly recommend using seperate cgminers for seperate gpu. You will have to make seperate config files (will explain later). But you want to set to "device" : "0" for your first gpu then 1,2,3 etc for others. If multiple gpu of the same types end up on the same settings you can run them in the same cgminer window, again much easier to tweak seperately though (Easier to mine seperate servers, coins etc).
Queue, Scan-Time and Expiry: All these settings have to do with the work being accepted and givin back to the server. In most cases you will see much less stales and generally better wu/m from setting queue=0 scan-time=1 and expiry=1. Its very difficult to see results from adjusting these settings but best to either set them that way and forget about it or set to stock. Seems to help on multipools more then others.
Those were all the settings you will be tweaking in cgminer to get the best results from your card. I will explain below how to set everything up but you will first need to download the miner. As mentioned above as far as I know Kalroth's release is the only one with xintensity. If you are not going to use xintensity then I recommend using sgminer. You can use the same settings for either one with only one minor difference I will mention below:
