Merge commit '576e22b' into cg_merges_20130513

Conflicts:
	README.scrypt

README.scrypt

@@ -1,12 +1,11 @@
 If you wish to donate to the author of scrypt support, Con Kolivas, please send
 your donations to:
 
-Bitcoin : 15qSxP1SQcUX3o4nhkfdbgyoWEFMomJ4rZ
+Bitcoin : 15qSxP1SQcUX3o4nhkfdbgyoWEFMomJ4rZ (preferred)
 Litecoin: Lc8TWMiKM7gRUrG8VB8pPNP1Yvt1SGZnoH
 
 ---
 
-
 Scrypt mining for GPU is completely different to sha256 used for bitcoin
 mining. 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
@@ -14,11 +13,10 @@ 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, BFGMiner will fail IN RANDOM WAYS. They are all due
-to parameters being outside what the GPU can cope with. Not giving BFGMiner a
-hint as to your GPU type, it will hardly ever perform well.
+There are 5 main parameters to tuning scrypt, all of which are optional for
+further fine tuning. When you start scrypt mining with the --scrypt option,
+BFGMiner will fail IN RANDOM WAYS. They are all due to parameters being outside
+what the GPU can cope with.
 
 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.
@@ -44,13 +42,31 @@ lines are in the .bat before starting cgminer:
 setx GPU_MAX_ALLOC_PERCENT 100
 setx GPU_USE_SYNC_OBJECTS 1
 
+--intensity XX (-I 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. High intensities
+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. Note that if you do NOT specify an
+intensity, cgminer uses dynamic mode which is designed to minimise the harm
+to a running desktop and performance WILL be poor. The lower limit to intensity
+with scrypt is usually 8 and cgminer will prevent it going too low.
+SUMMARY: Setting this for reasonable hashrates is mandatory.
+
 --shaders XXX
 
 is a new option where you tell BFGMiner how many shaders your GPU has. This
 helps BFGMiner 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.
+pointless trying to mine on. If this is not set, cgminer will query the
+device for how much memory it supports and will try to set a value based on
+that.
+SUMMARY: This will get you started but fine tuning for optimal performance is
+required.
 
 GPU  Shaders
 7750 512
@@ -84,35 +100,24 @@ These are only used as a rough guide for BFGMiner, 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 BFGMiner 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 BFGMiner 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.
+into --shaders and is ultimately a BETTER way to tune performance.
+SUMMARY: Spend lots of time finding the highest value that your device likes
+and increases hashrate.
+
+-g:
+Once you have found the optimal shaders and intensity, you can start increasing
+the -g value till BFGMiner fails to start. This is really only of value if you
+want to run low intensities as you will be unable to run more than 1.
+SUMMARY: Don't touch this.
 
 --lookup-gap
 This tunes a compromise between ram usage and performance. Performance peaks
@@ -120,6 +125,18 @@ 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 BFGMiner will use the --shaders value to choose
 a thread-concurrency if you haven't chosen one.
+SUMMARY: Don't touch this.
+
+
+Related parameters:
+--worksize XX (-w XX)
+Has a minor effect, should be a multiple of 64 up to 256 maximum.
+SUMMARY: Worth playing with once everything else has been tried but will
+probably do nothing.
+
+--vectors XX (-v XX)
+Vectors are NOT used by the scrypt mining kernel.
+SUMMARY: Does nothing.
 
 
 Overclocking for scrypt mining:
@@ -131,20 +148,23 @@ 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.
-
+you increase the engine clock speed further.
 
-Suggested values for 7970 for example:
-export GPU_MAX_ALLOC_PERCENT=100
---thread-concurrency 8192 -g 4 --gpu-engine 1135 --gpu-memclock 1375
+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!
 
 ---
 
 If you wish to donate to the author of scrypt support, Con Kolivas, please send
 your donations to:
 
-Bitcoin : 15qSxP1SQcUX3o4nhkfdbgyoWEFMomJ4rZ
+Bitcoin : 15qSxP1SQcUX3o4nhkfdbgyoWEFMomJ4rZ (preferred)
 Litecoin: Lc8TWMiKM7gRUrG8VB8pPNP1Yvt1SGZnoH