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If you wish to donate to the author, Con Kolivas, in LTC, please submit your
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donations to:
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Lc8TWMiKM7gRUrG8VB8pPNP1Yvt1SGZnoH
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Otherwise, please donate in BTC as per the main README.
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---
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Scrypt mining, AKA litecoin mining, for GPU is completely different to sha256
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used for bitcoin mining. The algorithm was originally developed in a manner
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that it was anticipated would make it suitable for mining on CPU but NOT GPU.
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Thanks to some innovative work by Artforz and mtrlt, this was proven to be
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wrong. However, it has very different requirements to bitcoin mining and is a
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lot more complicated to get working well. Note that it is a ram dependent
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workload, and requires you to have enough system ram as well as fast enough
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GPU ram. If you have less system ram than your GPU has, it may not be possible
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to mine at any reasonable rate.
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There are 5 main parameters to tuning scrypt, 2 of which you MUST set, and
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the others are optional for further fine tuning. When you start scrypt mining
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with the --scrypt option, cgminer will fail IN RANDOM WAYS. They are all due
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to parameters being outside what the GPU can cope with. Not giving cgminer a
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hint as to your GPU type, it will hardly ever perform well.
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NOTE that if it does not fail at startup, the presence of hardware errors (HW)
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are a sure sign that you have set the parameters too high.
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Step 1 on linux:
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export GPU_MAX_ALLOC_PERCENT=100
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If you do not do this, you may find it impossible to scrypt mine. You may find
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a value of 40 is enough and increasing this further has little effect.
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export GPU_USE_SYNC_OBJECTS=1
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may help CPU usage a little as well.
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--shaders XXX
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is a new option where you tell cgminer how many shaders your GPU has. This
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helps cgminer try to choose some meaningful baseline parameters. Use this table
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below to determine how many shaders your GPU has, and note that there are some
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variants of these cards, and nvidia shaders are much much lower and virtually
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pointless trying to mine on.
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GPU Shaders
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7750 512
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7770 640
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7850 1024
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7870 1280
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7950 1792
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7970 2048
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6850 960
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6870 1120
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6950 1408
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6970 1536
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6990 (6970x2)
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6570 480
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6670 480
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6790 800
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6450 160
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5670 400
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5750 720
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5770 800
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5830 1120
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5850 1440
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5870 1600
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5970 (5870x2)
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These are only used as a rough guide for cgminer, and it is rare that this is
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all you will need to set.
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--intensity XX
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Just like in bitcoin mining, scrypt mining takes an intensity, however the
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scale goes from 0 to 20 to mimic the "Aggression" used in mtrlt's reaper. The
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reason this is crucial is that too high an intensity can actually be
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disastrous with scrypt because it CAN run out of ram. Intensities over 13
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start writing over the same ram and it is highly dependent on the GPU, but they
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can start actually DECREASING your hashrate, or even worse, start producing
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garbage with HW errors skyrocketing. The low level detail is that intensity is
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only guaranteed up to the power of 2 that most closely matches the thread
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concurrency. i.e. a thread concurrency of 6144 has 8192 as the nearest power
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of two above it, thus as 2^13=8192, that is an intensity of 13.
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Optional parameters to tune:
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-g, --thread-concurrency, --lookup-gap
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-g:
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Once you have found the optimal shaders and intensity, you can start increasing
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the -g value till cgminer fails to start. Rarely will you be able to go over
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about -g 4 and each increase in -g only increases hashrate slightly.
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--thread-concurrency:
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This tunes the optimal size of work that scrypt can do. It is internally tuned
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by cgminer to be the highest reasonable multiple of shaders that it can
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allocate on your GPU. Ideally it should be a multiple of your shader count.
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vliw5 architecture (R5XXX) would be best at 5x shaders, while VLIW4 (R6xxx and
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R7xxx) are best at 4x. Setting thread concurrency overrides anything you put
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into --shaders.
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--lookup-gap
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This tunes a compromise between ram usage and performance. Performance peaks
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at a gap of 2, but increasing the gap can save you some GPU ram, but almost
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always at the cost of significant loss of hashrate. Setting lookup gap
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overrides the default of 2, but cgminer will use the --shaders value to choose
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a thread-concurrency if you haven't chosen one.
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Overclocking for scrypt mining:
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First of all, do not underclock your memory initially. Scrypt mining requires
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memory speed and on most, but not all, GPUs, lowering memory speed lowers
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mining performance.
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Second, absolute engine clock speeds do NOT correlate with hashrate. The ratio
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of engine clock speed to memory matters, so if you set your memory to the
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default value, and then start overclocking as you are running it, you should
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find a sweet spot where the hashrate peaks and then it might actually drop if
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you increase the engine clock speed further. Unless you wish to run with a
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dynamic intensity, do not go over 13 without testing it while it's running to
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see that it increases hashrate AND utility WITHOUT increasing your HW errors.
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Suggested values for 7970 for example:
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export GPU_MAX_ALLOC_PERCENT=100
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--thread-concurrency 8192 -g 4 --gpu-engine 1135 --gpu-memclock 1375
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---
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If you wish to donate to the author, Con Kolivas, in LTC, please submit your
|
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|
|
donations to:
|
|
|
|
|
|
|
|
Lc8TWMiKM7gRUrG8VB8pPNP1Yvt1SGZnoH
|
|
|
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Otherwise, please donate in BTC as per the main README.
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