[QUOTE=c10ck3r;338186]Okay, I have questions that have probably been asked time and time again: what is the minimum exponent that can be tested with mfaktc 0.20? What is the minimum bit depth? Maximum? Is there a maximum exponent testable by design, or just based on memory?
Thanks in advance![/QUOTE][quote]from: [url]http://mersennewiki.org/index.php/Mfaktc[/url]
Current limits[list][*]Prime exponents between 1,000,000 and 2[sup]32[/sup]-1[*]Factor sizes <2[sup]95[/sup] and k<2[sup]63.9[/sup][/list][/quote]Also:[list][*]GPU sieving is not available for < 2[sup]64[/sup] (the kernels that support such small factors are old (and notably slower than the more modern kernels available for "normal" GIMPS-range work) and haven't been rewritten to support GPU sieving)[/list]

Please see [URL]http://mersenneforum.org/showpost.php?p=344999&postcount=852[/URL]

I'm afraid this also applies to mfaktc, though I'm not sure if GPUSieveProcessSize=24 is commonly used here.

Oliver, can you check tf_common_gs.cu, the calculation of numblocks. I think the remainder of the division is lost.

on my little GT 640 I use GPUSieveProcessSize=8 ;)

[QUOTE=Bdot;345001]Please see [URL]http://mersenneforum.org/showpost.php?p=344999&postcount=852[/URL]

I'm afraid this also applies to mfaktc, though I'm not sure if GPUSieveProcessSize=24 is commonly used here.

Oliver, can you check tf_common_gs.cu, the calculation of numblocks. I think the remainder of the division is lost.[/QUOTE]

I guess mfaktc is affected, too. (What about mmff?)
For now I recommend to set GPUSieveSize to a multiple of GPUSieveProcessSize. Keep in mind that GPUSieveProcessSize is in Kibibits (1024 Bits) and GPUSieveSize in Mebibits (1048576 bits), thus GPUSieveSize=5 [B][U]is[/U][/B] a multiple of GPUSieveProcessSize=16.
[B]The only problematic setting is GPUSieveProcessSize=24 and GPUSieveSize not a multiple of 3[/B]. For all other valid settings of GPUSieveProcessSize (8, 16, 32) it doesn't matter which value you choose for GPUSieveSize because it will allways be a multiple of GPUSieveProcessSize.

Bertram: how do we fix this? The easy way by checking GPUSieveProcessSize and GPUSieveSize when the parameter file is read and autoadjust GPUSieveSize?

Oliver

[QUOTE=TheJudger;345194]
Bertram: how do we fix this? The easy way by checking GPUSieveProcessSize and GPUSieveSize when the parameter file is read and autoadjust GPUSieveSize?

Oliver[/QUOTE]
Yes, that's what I would prefer. I've sent you an email with my fix.

Other options include:
[LIST][*]run one more block that is only partially filled
(disadvantage: for every sieve block would would run a few thousand "useless" TF threads)[*]not advancing k_min at the end of the loop by mystuff->gpu_sieve_size * NUM_CLASSES, but by mystuff->gpu_sieve_processing_size * numblocks
(disadvantage: every sieve block would have an overlap with the previous one, and sieve a few thousand FCs again.)[*]I don't see a disadvantage in adjusting GPUSieveSize (except that it now may not be a nice power of two :smile:)[/LIST](above disadvantages apply only if GPUSieveProcessSize=24 && GPUSieveSize%3 > 0)

Edit: I also posted a note to the mmff thread now.

[QUOTE=Xyzzy;325305]FWIW, we played around with the values to find the most productive combo, and for both of our cards that combo was "GPUSieveSize=128" and "GPUSieveProcessSize=8".

YMMV[/QUOTE]

Me too, on a GT 430, and a GTX 760.

The GTX 760 went from 229 GHz/days/day to 249 GHz/days/day!

What is your GPUSievePrimes set to? I get best results with (GTX 580):

GPUSievePrimes=70000
GPUSieveSize=128
GPUSieveProcessSize=16

[QUOTE=flashjh;354357]What is your GPUSievePrimes set to? I get best results with (GTX 580):

GPUSievePrimes=70000
GPUSieveSize=128
GPUSieveProcessSize=16[/QUOTE]

GPUSievePrimes=82486

I haven't changed it from the default yet.

[QUOTE=Mark Rose;354365]GPUSievePrimes=82486

I haven't changed it from the default yet.[/QUOTE]
I get better output with 70K.

[QUOTE=flashjh;354367]I get better output with 70K.[/QUOTE]

Really! Which chip(s)? Any or all?

EDIT:
Boosted the 570 15-18 GHz-d/d at restart. Trailed off to 5-7 GHz-d/d.

Not very noticeable with the 580. Harder to say, as that one drives the display. It fluctuates more.

I can only speak for GTX 580 but it's not too hard to make changes to the number and see what you get.