Topic: another 3% mining increase with poclbm kernel.cl - page 3. (Read 9989 times)

This method actually caused a decrease of 30%. I went from 26.81 MHash/s down to 18.71 MHash/s.

TLDR - Probably yes, maybe not. Try it anyway

When mining, you're calculating SHA256( SHA256( w0,w1,... nonce ..., w15) ), where the w-s are some constants, most of which depend on the block you're trying to solve. The calculation of each SHA consists of two stages - the expansion (a.k.a. message schedule), which takes your input words w0 through w15, and expands them into 64 words, w0 through w63, and the compression, which iterates on these 64 expanded words 64 times, with each wi used only once, on iteration i. So.... There are at least two ways to carry out this calculation. 1 - expand the 16 original input words into 64 words, and then use them. 2 - expand these as necessary, i.e. calculate wi on the iteration i, when it is needed. My guess is that one kernel implements #1, and another implements #2. So, w[128] is probably the same as w0,w1... . It is also hard to tell which way is better, it depends on the compiler and your hardware (register pressure, scheduling and so on)... What I don't know is why they've got 128 words instead of 64; perhaps it is because of calculating the hash twice, or it could be because they're calculating two hashes at once, in parallel. Unfortunately, I don't have access to the source code at the moment, so all I can do is guess I hope this helps.

Thank you, you are a scholar and a gentleman (for finding and sharing this)

I'll try it out tonight and report my results, will definitely tip you if it helps!

Any idea if it would work with PhatK as well?

Normally I wouldn't try it without a truth table proof like bitless posted on his speedup, but since you're just making variables local to a function, it makes sense.  I'll try and report back!

edit: I noticed the PhatK kernel.cl doesn't contain the exact line to modify, I looked for W0 - W15 variables to make __local but I'm no OpenCL coder, so I can't find them if they even exist at all.

There's a u W[128] at the beginning of the Search() function, would those be the same as poclbm's w0-w15 ?

edit2: changed u W[128] to __local u W[128] and no change in hashrate (except from 217.5 -> 217.7 which could be noise), perhaps it's already compiling as local

you have to change this line in kernel.cl. tested this with poclbm kernel only.

   u W0, W1, W2, W3, W4, W5, W6, W7, W8, W9, W10, W11, W12, W13, W14, W15;
to
    __local u W0, W1, W2, W3, W4, W5, W6, W7, W8, W9, W10, W11, W12, W13, W14, W15;

basically, add a  __local  key keyword to this line and it should increase your performance.