Bitcoin 7950

In a previous blog article, I wrote about “bitcoin” mining (really scrypt coins) on a 7970. The 7970 model runs really well with two gpu-threads in cgminer but the earlier model, the 7950, struggles with two threads.

Up until recently, the general practice with a 7950 was to push really high intensity values (18+) until reject rates get out of hand (more than 2%). While people with MSI brand cards report seeing over 700KH/s with these settings, I was not.

Here is my original cgminer configuration using the official version 3.7.2.

cgminer –scrypt -I 19 -w 256 -g 1 –thread-concurrency 16384 –-gpu-powertune 20 –-gpu-engine 1025 –-gpu-memclock 1525

Notice how above we are using a single gpu thread and pushing it almost to the max with intensity. I’ve played with lower and higher thread count numbers, but for me, 16384 seemed to be the sweet spot. Also, without –gpu-powertune 20, the card would immediately throttle to about 70% usage after 30 seconds of running, causing the hashrates to drop. With these basic settings, I could get my 7950 to run at approximately 620 KH/s. If I pushed intensity to 20, I could get as high as 643 KH/s, but my reject rates were over 6%, which is no good.

I was often saddened that my 7950 costs the same amount of electricity as my 7970, but could not reach 700 KH/s, like my 7970. The 7950 also ran hotter, most likely due to the heavy intensity and high clock speeds.

I almost gave up until I ran into Kalroth’s version of cgminer. This version of cgminer introduces a new way to control intensity called xintensity. You can read the README.txt that comes with the download if you want to understand the differences, but the end result is that I can run two threads at a lower temperature and a faster hash rate!

cgminer –scrypt -X 4 -w 256 -g 2 –thread-concurrency 16384 –gpu-powertune 20 –-gpu-engine 1025 –-gpu-memclock 1525

Remember, not everyone will have the same results. My 7950 card is listed on NewEgg as the SAPPHIRE 11196-16-CPO Radeon HD 7950 3GB 384-bit GDDR5 PCI Express 3.0 x16 CrossFireX Support Video Card. Your mileage will of course vary.