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SETI MB CUDA for Linux
b0b3r:
--- Quote from: riofl on 01 Oct 2009, 11:45:43 am ---hmm yeah ... my basis is on integer gflops since i have not found double precision gflops comparisons. basing performance comparisons between my tesla at 933 integer gflops and my 285 at 1062 integer gflops, boinc displays them as 74 and 127 gflops respectively. now, considering the 295 is slower in integer gflops per processing system (894 each) than the tesla, i would expect it would display less than 74gflops each half.
which basically means that for a given card, a 295 using both halves will only give approximately 50-60% higher performance in total then a single 285 which makes me curious about its value other than accepting that 50% more per physical device is preferable. i just wonder if since the 295 is essentially supposed to be 2x 285 with slightly degraded performance why it is so? it has 4 less pixel shaders (28 vs 32) and smaller memory bus width (448 vs 512 which to me is the most major item). although these vary by mfgr, in general the 295 also has slower default clock speeds. admittedly lower clock speeds will help with eliminating heat buildup, but instead of using the same default heatsink assy, put a better designed one on to compensate and keep the performance up. guess i just wonder why its design doesn't make a lot of sense or maybe i am in wishful thinking mode that it 'should' be a 2x full 285 units when in fact it is 2x crippled 285 units.
--- End quote ---
First there is no such a thing like a "integer gflops". There are single (32bit) or double (64bit) precision floating-point operations. And indeed double precision performance is about 8 times lower than single in nvidia gpus. The reason why each of gpus on 295 is slower clocked is heat production. Following documentation it is 290W for two gpus on 295 card. For 285 it is about 205W for single GPU. So considering this card with two 285 with normal clocks may produce over 410W of heat power. It is very hard to dissipate that much heat. Even 295 with it's 290W is a very hot card and need very good cooling to stable work. Asus card from the link is build with two full clocked 285 chip and its cooling system is very big. It take 2.5 slots.
Difference in number of pixel shader is not important for CUDA computing. It uses vertex shader which both have 240 organized in 30 stream processors to use with CUDA (8 shader in each). Memory is faster 159GB/s (285) vs 112GB/s (for single gpu on 295) and shader clock is faster in 285. And again following documentation theoretical peak single precision performance for 285 is 1062Gflop/s (about 130Gflop/s in double) and for 295 895Gflop/s (about 112Gflop/s in double) for each gpu. Difference is about 15% but what is a difference for real computation time. Unfortunately I don't have any 285 card to do a test but i have 275 and 260sp216. Theoretical difference is over 25% (275 - 1010Gflop/s, 260 - 804Gflop/s) but real computation time for Seti is about 670 sec. for 275 and about 750 sec. for 260 (with normal 0.44 ar. unit). So the real difference is little over 10% like I said before.
What I try to say is that each of gpu's on 295 are theoretically about 15% slower compared to 285. But in real computation each of 295 gpu will be slower only about 5% to 6%. So with 295 we have more than 185% performance of 285 with not so big difference in price. :)
riofl:
ahh... thanks. makes sense. i have a nasty habit of thinking myself into corners. unfortunately that asus mars is untouchable for me. just way too much $$. 295 does sound like the way to go and i think i have enough air flow around the gpus to keep it cool. my 285 and tesla both never go above 65c with a summer room ambient temp of 28c. took running the fans at 100%, adding extra bottom front fan to move cooler air into the lower case pocket plus a few small pci slot exhaust fans. with the spacing of my mobo's pcie slots it is not easy getting the extra heated air out from between the 2 cards. had to mount a little 1 in fan on the tops of the cards aiming between them to move the air out which dropped both card temps quite a bit. probably would have been eaiser to buy another case side cover with fans directly over the gpus. mine has a single 25cm fan in the middle of the cover.
b0b3r:
I also advise to wait for g300. It's premiere may greatly change prices of 295. :)
Tye:
I've been using BOINC 6.6.11 for awhile now, to make sure it handles my multi-GPUs of different types. Is there any newer version that will also do this yet? Sunu, I think you were also using 6.6.11...
pp:
I've been using the 6.10.x series for a while and it works correctly with multiple GPUs. Use at least 6.10.7 and upwards because previous versions introduced some new bug that preempted all CUDA tasks.
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