I have a very strange (to me) thing going on with my 7970's. Let me start off with some of my hardware\OS\driver stats:
OS: Win7 x64
GPU's: Sapphire 7970 OC - (11197-03-40G) (
http://www.amazon.com/gp/product/B009B6Y01Y)
RAM: 8GB
AMD Driver: 13.1
SDK: 2.7
I have gone through all the threads that discuss getting the 7970 running optimized for Scrypt mining:
1)
https://bitcointalk.org/index.php?topic=117221.msg1256502#msg12565022)
https://bitcointalk.org/index.php?topic=173938.03)
https://bitcointalk.org/index.php?topic=28402.msg1635964#msg16359644) and many others, but those are the main ones.
So just using stock voltages (don't want to mess with tweaking those), I was able to determine by highest stable memory settings for me are 1625. I ended up using these settings to allow cgminer to find me some good numbers:
cgminer.exe --scrypt -o stratum+tcp://pool.com:3333 -u Jazkal -p X --intensity 13 -g 2 --thread-concurrency 8192 --lookup-gap 2 --gpu-powertune 20 --auto-fan --auto-gpu
With this, I was able to boost my numbers from low 525 or so to 630-650. Looking at what cgminer defaulted to, it choose 950/1625. Sometimes if would choose 1650 which would crash the system. So I tweaked around and found that 1650 was the outside edge of stability for this card. So I added a hard code for 1625 which seemed to run just fine and was stable.
Now since I run my rigs out in an outdoor shed in the middle of the Texas summer heat (100F+), I let cgminer change up my settings downward when the heat climbs. So I was adding in this setting:
--gpu-memclock 1000-1625
This is what I find strange...
And when I re-launched cgminer, it defaulted to 950/1000 but was still running at 630-650 stable.
Why would it run at the same hashing power at 950/1000 and 950/1625? This doesn't make any sense to me. Can someone help me understand why this is? I thought Scrypt mining was all about super high memory settings.
edit: forgot to add my driver and sdk info
