Overclocking for scrypt mining:
First of all, do not underclock your memory initially. Scrypt mining requires
memory speed and on most, but not all, GPUs, lowering memory speed lowers
Second, absolute engine clock speeds do NOT correlate with hashrate. The ratio
of engine clock speed to memory matters, so if you set your memory to the
default value, and then start overclocking as you are running it, you should
find a sweet spot where the hashrate peaks and then it might actually drop if
you increase the engine clock speed further.
Third, the combination of motherboard, CPU and system ram ALSO makes a
difference, so values that work for a GPU on one system may not work for the
same GPU on a different system. A decent amount of system ram is actually
required for scrypt mining, and 4GB is suggested.
Finally, the power consumption while mining at high engine clocks, very high
memory clocks can be far in excess of what you might imagine.
For example, a 7970 running with the following settings:
--thread-concurrency 22392 --gpu-engine 1135 --gpu-memclock 1890
was using 305W!
TUNING AN AMD RADEON 7970 or really any GPU for that matter
Example tuning a 7970 for Scrypt mining:
On linux run this command:
or on windows this:
setx GPU_MAX_ALLOC_PERCENT 100
in the same console/bash/dos prompt/bat file/whatever you want to call it,
before running cgminer.
First, find the highest thread concurrency that you can start it at. They should
all start at 8192 but some will go up to 3 times that. Don't go too high on the
intensity while testing and don't change gpu threads. If you cannot go above
8192, don't fret as you can still get a high hashrate.
Delete any .bin files so you're starting from scratch and see what bins get
First try without any thread concurrency or even shaders, as cgminer will try to
find an optimal value
cgminer -I 13
If that starts mining, see what bin was generated, it is likely the largest
meaningful TC you can set.
Starting it on mine I get:
See tc22392 that's telling you what thread concurrency it was. It should start
without TC parameters, but you never know. So if it doesn't, start with
--thread-concurrency 8192 and add 2048 to it at a time till you find the highest
value it will start successfully at.
Then start overclocking the eyeballs off your memory, as 7970s are exquisitely
sensitive to memory speed and amazingly overclockable but please make sure it
keeps adequately cooled with --auto-fan! Do it while it's running from the GPU
menu. Go up by 25 at a time every 30 seconds or so until your GPU crashes. Then
reboot and start it 25 lower as a rough start. Mine runs stable at 1900 memory
without overvolting. Overvolting is the only thing that can actually damage your
GPU so I wouldn't recommend it at all.
Then once you find the maximum memory clock speed, you need to find the sweet
spot engine clock speed that matches it. It's a fine line where one more MHz
will make the hashrate drop by 20%. It's somewhere in the .57 - 0.6 ratio range.
Start your engine clock speed at half your memory clock speed and then increase
it by 5 at a time. The hashrate should climb a little each rise in engine speed
and then suddenly drop above a certain value. Decrease it by 1 then until you
find it climbs dramatically. If your engine clock speed cannot get that high
without crashing the GPU, you will have to use a lower memclock.
Then, and only then, bother trying to increase intensity further.
My final settings were:
--gpu-engine 1141 --gpu-memclock 1875 -I 20
for a hashrate of 745kH.
Note I did not bother setting a thread concurrency. Once you have the magic
endpoint, look at what tc was chosen by the bin file generated and then hard
code that in next time (eg --thread-concurrency 22392) as slight changes in
thread concurrency will happen every time if you don't specify one, and the tc
to clock ratios are critical!
Good luck, and if this doesn't work for you, well same old magic discussion
applies, I cannot debug every hardware combo out there.
Your numbers will be your numbers depending on your hardware combination and OS,
so don't expect to get exactly the same results!