My previous article on Litecoin mining I discussed how you can get started mining Litecoins, an alternative to the Bitcoin crypto-currency, using your spare CPU cycles. If you’re GPU is already mining Bitcoins, using your CPU to mine Litecoins may be an obvious choice. However, if you are “all in” on Litecoin then you can get a sizable performance increase by using your GPU to mine Litecoins. Whether that trade-off is worth-while is a decision you would need to make. Litecoin is not as mature as Bitcoin and is just as volatile. Some see it as a doomed clone, others as the next Bitcoin, poised to take off.
In order to start using your GPU to mine Litecoins on OS X, you’ll need to first install cgminer or bfgminer. Please read my previous article on Bitcoin mining for step-by-step instructions and installation packages for cgminer and bfgminer. The Homebrew formulas I shared in my previous article include the configuration settings necessary to mine both Bitcoins and Litecoins. If you are compiling the applications yourself, make sure to use the –enable-scrypt parameter when running ./configure.
Armed with a copy of cgminer or bfgminer with scrypt enabled, you can now start mining Litecoins with your GPU. Now a fair warning: finding a nice set of parameters for mining Litecoins with cgminer or bfgminer is far more finicky and time consuming. With Bitcoins you can basically run either miner and just specify your pool. The miner will then tune itself and eventually reach a nice hash-rate.
This isn’t really the case with using either miner to mine Litecoins. For instance, if I use the following command line to mine Litecoins using my ATI 5770. Note that I am using the -d parameter to specify which GPU to use to simplify these examples.
cgminer --scrypt -o host:port -u username -p password -d 0
With no additional tuning my 5770 gets about 5Kh/s. My CPU alone gets around 29Kh/s. Using bfgminer with the basic command-line parameters yields similar results. As indicated in my previous article I use the –no-opencl-binaries to work around a crash in bfgminer with multiple GPU’s on OS X.
bfgminer --scrypt -o host:port -u username -p password -d 0 --no-opencl-binaries
So how can we get better performance mining Litecoins on the GPU? The first parameter to focus on is the -I parameter, or the intensity. With Bitcoin this parameter does help, but honestly not a ton. If you aren’t using the PC, and you leave the intensity at “Desktop” (-I d), both cgminer and bfgminer will eventually reach around the same performance you’d get by specifying something like -I 9.
This is not the case with Litecoin mining. With scrypt (Litecoin’s hashing algorithm) you need to specify a high intensity, in fact higher than is suggested for Bitcoin. I’d start at around 10 and go up from there. On my system, 15-16 is about the best I can do.
So lets try cgminer with -I 13 to see what that does:
cgminer --scrypt -o host:port -u username -p password -d 0 -I 13
That change alone triples the Kh/s, but from 5Kh/s to 15Kh/s honestly isn’t much to brag about. Let’s try with bfgminer:
bfgminer --scrypt -o host:port -u username -p password -d 0 --no-opencl-binaries -I 13
Similarly I get around 14Kh/s using the -I 13 parameter with bfgminer.
The next parameter to focus on is the -w parameter, which specifies a worksize in multiples of 64 up to 256. This parameter is what really makes a difference on my OS X rig:
cgminer --scrypt -o host:port -u username -p password -d 0 -I 13 -w 64
Now we’re cooking with Crisco! Using -I 13 -w 64 on my 5770 gets me from the original 5Kh/s up to 83Kh/s with cgminer. And with bfgminer?
bfgminer --scrypt -o host:port -u username -p password -d 0 --no-opencl-binaries -I 13 -w 64
This gets us up to around 80 Kh/s with bfgminer as well. By removing the -d parameter so that both GPU’s are used and cranking up the -I parameter to 16 I can get my GPU’s up to around 230 Kh/s:
cgminer --scrypt -o host:port -u username -p password -I 16 -w 64
The last parameter I want to note is –thread-concurrency. If cgminer or bfgminer are reporting hardware errors (the HW number in the output) this indicates that you need to make use of the –thread-concurrency parameter. These are not hardware failures. You can find guidelines for the value to use here:
57xx cards: 2368-4096 (3200 is common)
58xx cards: 4096-8192 (5600, 7168, and 8000 are common)
5970 cards: 4096-8192 (5632 or 8000 are common)
67xx cards: 2368-4096 (3200 is common)
68xx cards: 3008-6720 (4800 is common)
69xx cards: 4096-8192 (5600, 7168, and 8000 are common)
6990 cards: 4096-8192 (5632 or 8000 are common)
7xxx cards: 64 * bus-width-of-card-in-bits. So, for a 7950, that would be 64 * 384 = 24576. Ideal values are 21712 or 24000. Find your bus width here.
I verified that 3200 works well with a 5770 and 4800 works well with a 6870.
And that about covers it for my series of articles on mining Bitcoins and Litecoins using Mac OS X and Apple hardware. The growing landscape of crypto-currency is fascinating from many perspectives. If your interest is piqued and you are running OS X, hopefully you now have the information you need in order to get started mining this new form of currency.