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HassanShebli

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Message 46016 - Posted: 6 Feb 2011, 14:59:00 UTC

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ProfileKeith Myers
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Message 46017 - Posted: 6 Feb 2011, 16:07:12 UTC - in response to Message 46016.  

Don't have multiple cards, yet. I am still deciding whether my current new power supply will support two GTX460's. To answer your question, yes, more cards means more work can be done per machine. Since I saw such a dramatic increase when I just went to a GPU, I am already wanting to add another GPU to double my RAC. I am getting more work out of the GPU than the quad CPU. To answer your implied question whether adding more cards means you will get faster crunching, I think I know what you mean, no, you will not crunch WU's any faster as regard to completion times, you will just do more work per day with more cards.

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Message 46019 - Posted: 6 Feb 2011, 16:27:21 UTC

Short answers:

* Compared to a single GPU: Yes.
* Compared to the same number of GPUs enabled without the use of CF or SLI: No.

BOINC has the same potential as with F@H. But remember, you don't need CF or SLI to use multiple GPUs (except for games and other 3D rendering).

To try and sort a misunderstanding from another thread, there are at least two ways to enable multiple GPUs:

1. Disable CF/SLI, connect a monitor or a dummy plug (connector with 3 resistors) to each, and miroor or extend the desktop onto all. This yields performance scaling as good as it gets (but games will use only one card).

2. Enable CF/SLI. BOINC will still see separate GPUs and scale performance well, possibly (probably!) with a small overhead not used for crunching.

Even though multiple cards offer close to 100% performance scaling in BOINC (no matter how you enable them), the statement that CF/SLI isn't beneficial to BOINC has merit. Compared to the same number of GPUs enabled separately (option 1 above), CF/SLI offers no performance gain. More like marginally less performance. But it used to be far worse...

I have no experience with BOINC on SLI, but CF has come a long way since I kept sending Cluster Physik my CF test reports (which he deserves credit for even making sense of). Back then, two GPUs in CF would yield LESS crunching performance than one single GPU would, mainly because one GPU would fail to step up from idle clocks. In a later Catalyst driver release, that problem was solved, and the performance was SLIGHTLY better than a single GPU. The surplus computing potential would go unused: Low GPU usage, low power consumption. Nowadays, all that has been thoroughly ironed out by ATI/AMD, and GPU usage in CF is roughly on par with single GPUs. In fact, I notice less difference in MW WU times than the normal variation between WUs (only there are more WUs crunched simultaneously).

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KWH*
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Message 46021 - Posted: 6 Feb 2011, 19:44:43 UTC

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HassanShebli

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Message 46024 - Posted: 6 Feb 2011, 21:50:33 UTC

Thanks for everybody.

How about single cards with two GPUs? is it better?
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Zydor
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Message 46025 - Posted: 6 Feb 2011, 22:51:59 UTC - in response to Message 46024.  
Last modified: 6 Feb 2011, 22:59:44 UTC

I run 2x5970s in a 1090T box, as indicated above there is a small overhead - circa 2-5% - varies with the prevailing wind :)

The 5970(twin GPU) has the same GPU as a 5870 (single GPU), and as a general rule 2x5870s will outperform a 5970. The 2x5870 will also use considerably more power and take up more slot space in a box. So at the end of the day it depends where your individual priorities lay.

You'll be hard pressed to run 4x5870s in a box (not impossible by any means, perfectly achieveable), running 2x5970s is more efficient overall in terms of space, power etc. You could also take the view that since most will run 2x5870s in a box, running 2x5970s saves buying another box.

Which way an individual goes depends what an individual's priority is .... me,I'm bone idle, and running 2x5970s in one box was easier for me that battling with 4x5870s in a box, or buying another box to run2x5870s in each box.

Overall running 2x5970 Crossfire compared to 4x5870 will result in the 4x5870s winning out by around 2 to 3% overall in terms of performance only - ignoring the additional costs of more boxes for the 5870s, additional cost of the 4x5870s, and additional power drain from 4x5870s.

Pays your money, takes your choice as they say

Regards
Zy
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John Clark

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Message 46026 - Posted: 6 Feb 2011, 23:07:44 UTC

Something that can keep a PC as a single GPU system is the aftermarket cooler that replaces a failed stock cooler. I used an Arctic 3 x 120 mm fan system and the GPU runs at 45C all the time under DNETC load.

The down side is the GPU, with cooler, is so long that I had to hacksaw out 3 hard drive bays as the card stretched 2.5" inside the bay area. The width of the cooler, with the HD5850 in the primary graphics slot, covers 2 of the 3 remaining PCIe slots.

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ProfileBladeD
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Message 46528 - Posted: 11 Mar 2011, 3:23:22 UTC - in response to Message 46026.  

With CF, no monitor or dummy plug is needed on the second card.
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Message boards : Number crunching : Does Crossfire or Sli means more WUs crunching ?

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