FAQ cgminer for litecoin - - Криптовалюты - zx896
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    FAQ cgminer for litecoin
    Scrypt mining, AKA litecoin mining, for GPU is completely different to sha256
    used for bitcoin mining. The algorithm was originally developed in a manner
    that it was anticipated would make it suitable for mining on CPU but NOT GPU.
    Thanks to some innovative work by Artforz and mtrlt, this was proven to be
    wrong. However, it has very different requirements to bitcoin mining and is a
    lot more complicated to get working well. Note that it is a ram dependent
    workload, and requires you to have enough system ram as well as fast enough
    GPU ram. If you have less system ram than your GPU has, it may not be possible
    to mine at any reasonable rate.

    There are 5 main parameters to tuning scrypt, 2 of which you MUST set, and
    the others are optional for further fine tuning. When you start scrypt mining
    with the --scrypt option, cgminer will fail IN RANDOM WAYS. They are all due
    to parameters being outside what the GPU can cope with. Not giving cgminer a
    hint as to your GPU type, it will hardly ever perform well.

    NOTE that if it does not fail at startup, the presence of hardware errors (HW)
    are a sure sign that you have set the parameters too high.


    Step 1 on linux:
    export GPU_MAX_ALLOC_PERCENT=100
    If you do not do this, you may find it impossible to scrypt mine. You may find
    a value of 40 is enough and increasing this further has little effect.

    export GPU_USE_SYNC_OBJECTS=1
    may help CPU usage a little as well.

    --shaders XXX

    is a new option where you tell cgminer how many shaders your GPU has. This
    helps cgminer try to choose some meaningful baseline parameters. Use this table
    below to determine how many shaders your GPU has, and note that there are some
    variants of these cards, and nvidia shaders are much much lower and virtually
    pointless trying to mine on.

    GPU Shaders
    7750 512
    7770 640
    7850 1024
    7870 1280
    7950 1792
    7970 2048

    6850 960
    6870 1120
    6950 1408
    6970 1536
    6990 (6970x2)

    6570 480
    6670 480
    6790 800

    6450 160

    5670 400
    5750 720
    5770 800
    5830 1120
    5850 1440
    5870 1600
    5970 (5870x2)

    These are only used as a rough guide for cgminer, and it is rare that this is
    all you will need to set.


    --intensity XX

    Just like in bitcoin mining, scrypt mining takes an intensity, however the
    scale goes from 0 to 20 to mimic the "Aggression" used in mtrlt's reaper. The
    reason this is crucial is that too high an intensity can actually be
    disastrous with scrypt because it CAN run out of ram. Intensities over 13
    start writing over the same ram and it is highly dependent on the GPU, but they
    can start actually DECREASING your hashrate, or even worse, start producing
    garbage with HW errors skyrocketing. The low level detail is that intensity is
    only guaranteed up to the power of 2 that most closely matches the thread
    concurrency. i.e. a thread concurrency of 6144 has 8192 as the nearest power
    of two above it, thus as 2^13=8192, that is an intensity of 13.


    Optional parameters to tune:
    -g, --thread-concurrency, --lookup-gap

    -g:
    Once you have found the optimal shaders and intensity, you can start increasing
    the -g value till cgminer fails to start. Rarely will you be able to go over
    about -g 4 and each increase in -g only increases hashrate slightly.

    --thread-concurrency:
    This tunes the optimal size of work that scrypt can do. It is internally tuned
    by cgminer to be the highest reasonable multiple of shaders that it can
    allocate on your GPU. Ideally it should be a multiple of your shader count.
    vliw5 architecture (R5XXX) would be best at 5x shaders, while VLIW4 (R6xxx and
    R7xxx) are best at 4x. Setting thread concurrency overrides anything you put
    into --shaders.

    --lookup-gap
    This tunes a compromise between ram usage and performance. Performance peaks
    at a gap of 2, but increasing the gap can save you some GPU ram, but almost
    always at the cost of significant loss of hashrate. Setting lookup gap
    overrides the default of 2, but cgminer will use the --shaders value to choose
    a thread-concurrency if you haven't chosen one.


    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
    mining performance.

    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. Unless you wish to run with a
    dynamic intensity, do not go over 13 without testing it while it's running to
    see that it increases hashrate AND utility WITHOUT increasing your HW errors.
    Категория: Bitcoin | Добавил: zx896 (12.11.2012)
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