My rig (Nyx) is very stable as long as I don't turn on SLI. Once I turn on SLI, all hell seems to break loose.

Now, technically, I'm willing to run without SLI mode turned on, as I don't really need it, but it doesn't make sense that it should destabilize my system this much. So worse comes to worse, I'll just leave it off... but if you more experienced folks can help out, then all that much better.

Both CPU and GPUs are OC'd (GPUs at 840/1680/1900) but has exhibited same behavior at factory clock settings. It is water-cooled so running relatively cool at between 38-44 Celcius depending on ambient temps. So I don't believe its a heat issue either. I'm running 2 tasks/card, normally putting GPU usage at 88-90%. GPU memory usage is around 560mb.

I've dedicated 2 cpus (1 full core) to GPU tasks, so i'm only crunching CPU tasks on 10 cpus. Oh, and I'm running Lunatic's optimized apps for CPU and GPU.


Some of the symptoms I've seen once I turn SLI mode on:
- after a while of crunching, GPU usage drops down to 30% instead (EVGA precision doesn't show clock speeds changing when this happens).
- normally I can crunch GPU/CPU full steam and still use computer for email, surfing, video watching etc. But in SLI mode i have to shut down GPU crunching as the system becomes significantly more unusable with SETI on.
- just recently it started spewing errors immediately upon WU start, and once that started, it didnt stop. I had to quickly shut down SETI and disable SLI.

Example errors:
1780568665
1780554454

Some are OOM errors, others something else. Tried to catch it as fast as i could to shut it down. Disabled SLI, and was back to normal again.

Any suggestions/help would be appreciated!

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Try turning off Hyperthreading.

Cheers.

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What changes, when using SLI, is that u get work data of all running units copied in each cards memory. If u run 4 tasks(2 per cards), 330 MB each, u are out of memory(4x330). I'm not sure, but if it gets memory shortage, perhaps it starts to use system memory and thats why u get these slow downs.
There is no win-win solution. Either don't run SLI mode or just run one WU per cards(technically u can run one WU on one card and two on another, bcs of, I guess, each card has 1 GB).

I guess SLI runs fine with games etc. and problem is related only to SETI, right?

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Yes, seti has always had a bit of a problem with SLI. I have dual MSI GTX 460 HAWX in NON-SLI and I run 4 units at the same time (2 per card). Yes, I lose out on 3D performance, but if I want to play a game on that computer, all I have to do is restart in SLI mode and I'm good to go. So, for seti, run non-sli, it'll make your life a whooooole lot easier (and faster). :)

Happy Crunching!

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-baron_iv
Proud member of:
GPU Users Group

I may try dropping to 1 task/card just to confirm, but it may be that yeah, i just have to keep switching SLI on/off. Will probably just keep it off, since the GTX640 seems to handle any game quite well. without help.

Thanks for the input, will let you know if there are further developments!

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From my understanding when you run SLi only one card will crunch. So when you have it setup for 4 WU's all four are being transferred to one card. And like hbomber said (4x330) is more memory then one of your cards have available. So simply go into your control panel and disable SLi when crunching and when you want to play a game enable it. Another thing to look at is HT has been known to cause issues on various machine. I know Steve was having some issue with it on, not sure if what was affecting his machine is the will affect yours as he runs a wildly different setup but it's worth checking into as well.

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Traveling through space at ~67,000mph!

Both cards crunch is SLI mode. They just mirror memory contents.
Other noticeable thing which happens, it is they get their order swapped as CUDA devices. At least I observed last thing with some drivers before. But it can be checked easily.

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From my understanding when you run SLi only one card will crunch.

I believe this was a problem earlier, but has been overcome with current drivers.

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"Freedom is just Chaos, with better lighting." Alan Dean Foster

From my understanding when you run SLi only one card will crunch.

I believe this was a problem earlier, but has been overcome with current drivers.

Ah gotcha, so it's merely a matter of memory now then? So can you crunch 4 WUs in SLi if you have 1.5-2GB cards?

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Traveling through space at ~67,000mph!

From my understanding when you run SLi only one card will crunch.

I believe this was a problem earlier, but has been overcome with current drivers.

Ah gotcha, so it's merely a matter of memory now then? So can you crunch 4 WUs in SLi if you have 1.5-2GB cards?

I believe that is true. I have left SLI turned off on my dual card rigs anyway, as I don't do any gaming.

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"Freedom is just Chaos, with better lighting." Alan Dean Foster

Well I'll just leave SLI off. I was only trying to get it fixed because I thought there might be something wrong with the setup and I was concerned.

I do game a bit, but SLI isn't really needed. As someone mentioned out there, SLI is more for bragging rights anyway! It's happily crunching 2/card with SLI off, i'm ok with that.

I will go follow up on the discussions regarding hyperthreading. I'm not having problems that I know of, but worth checking out to see if its really helping or not.

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