Bottlenecking 250GTS SLI?

GoogalyMoogaly · 25 Nov 2010 at 20:26

Hi,

I've been reading a fair amount lately on these forums about CPUs bottlenecking GPUs. Specifically Dual Cores vs. Quad Cores.

This started me thinking, could my C2D E6850 @ Stock (3GHz) be bottlenecking my 250GTS SLI setup?

I've done some runs with the free version of 3DMark06.
With 1 1GB 250GTS card in I get about 12000 (roughly).
With 2 1GB 250GTS in SLI I get about 14000 (again, roughly).

Now I was under the impression that SLI scaled better than that!

My initial thought was that since I've got an old motherboard doing SLI means I have to run both lanes at 8x instead of 16x. Since the board is old it's PCI-e v1.0 (or whatever) so I thought it was a bandwidth issue.

Then I thought that it was because 3DMark06 only runs at 1280*1024 that it wasn't pushing the 2 cards enough to display a difference.

But now I'm wondering if it's my CPU not feeding the cards quick enough.

So could my E6850 be holding back my 250SLI or are 250GTS cards in SLI not that 'hungry'?

Thanks.

lay-z-boy · 25 Nov 2010 at 21:07

GoogalyMoogaly said:
3DMark06

Play a game instead.

MeatLoaf · 25 Nov 2010 at 22:14

Try with vantage bit really the best tests are games themselves. Grab the crysis demo and do the crysis benchmank

chipps101 · 26 Nov 2010 at 00:17

i had a similar problem a few days ago, i was testing my new 8800gt sli test machine with an athlon x2 4200+ @ 2.5 and running the unigine tropics benchmark.

at the default 1024 x 768 setting running the cards in sli actually scored less than a single card, by turning the resolution up to 1280 x 1024 and maxing the AA and AF settings the cpu no longer became the bottleneck and sli started scaling properly.

try a benchmark that you can turn the graphics settings up as high as possible in and you should see the difference between 1 card and sli

Rroff · 26 Nov 2010 at 00:22

Core 2 duo at 3gig won't (significantly) bottleneck a GTS250 SLI setup for gaming tho you won't see the max possible results from that GPU setup in benchmarks.

allday247 · 26 Nov 2010 at 10:05

Why are you even using that PC mate?! you have 4 other high spec gaming PC's that way surpass the components mentioned here. Ditch the old machine and use your newer PC's (btw i know a good charity you can donate those components to... me

)

GoogalyMoogaly · 27 Nov 2010 at 15:02

allday247 said:
Why are you even using that PC mate?! you have 4 other high spec gaming PC's that way surpass the components mentioned here. Ditch the old machine and use your newer PC's (btw i know a good charity you can donate those components to... me )

2 main reasons.
1) The PC generally seems to work fine so don't want to give it away, but would like to make sure it's working as well as possible.
2) It's the quietest PC I have and so is useful if I'm also trying to watch TV or alternating between TV and PC. But mostly reason 1.

And it's only 2 other PCs with higher specs

Peter450 · 27 Nov 2010 at 15:14

GoogalyMoogaly said:
Hi,

I've been reading a fair amount lately on these forums about CPUs bottlenecking GPUs. Specifically Dual Cores vs. Quad Cores.

This started me thinking, could my C2D E6850 @ Stock (3GHz) be bottlenecking my 250GTS SLI setup?

I've done some runs with the free version of 3DMark06.
With 1 1GB 250GTS card in I get about 12000 (roughly).
With 2 1GB 250GTS in SLI I get about 14000 (again, roughly).

Now I was under the impression that SLI scaled better than that!

My initial thought was that since I've got an old motherboard doing SLI means I have to run both lanes at 8x instead of 16x. Since the board is old it's PCI-e v1.0 (or whatever) so I thought it was a bandwidth issue.

Then I thought that it was because 3DMark06 only runs at 1280*1024 that it wasn't pushing the 2 cards enough to display a difference.

But now I'm wondering if it's my CPU not feeding the cards quick enough.

So could my E6850 be holding back my 250SLI or are 250GTS cards in SLI not that 'hungry'?

Thanks.

I would say probably not that much, 250's in SLI correct me if i'm wrong, but i think there about as fast as a 280GTX or there abouts

I think if you can get your dual core to 3.4 or more, it wont be, at 3ghz it might be a little, but only in certain games

I had a dual core at 3.8 and a GTX 280, and gamed at 1650x1080 and felt, they were a fair match, with neither really holding the other back, except maybe in Bad Company which i hear does fair better on Quads

GoogalyMoogaly · 27 Nov 2010 at 15:24

Peter450 said:
I would say probably not that much, 250's in SLI correct me if i'm wrong, but i think there about as fast as a 280GTX or there abouts

I think if you can get your dual core to 3.4 or more, it wont be, at 3ghz it might be a little, but only in certain games

I had a dual core at 3.8 and a GTX 280, and gamed at 1650x1080 and felt, they were a fair match, with neither really holding the other back, except maybe in Bad Company which i hear does fair better on Quads

I'd like to overclock the CPU to see if that helped, but unfortunately in my wisdom all those years ago I bought a motherboard using the nForce 650i SLI chipset. It seems to be unoverclockable

I think 250 SLI is basically the Nvidia 9800GX2 but with more memory. Not sure quite how that compares to the 200 series cards but I would guess 280GTX probably isn't far off.

chipps101 · 27 Nov 2010 at 15:36

have you tried them in anything other than 3dmark yet ?

i've been trying different resolutions and settings in tropics with my setup and the higher you turn the gfx options up the more you take the cpu out the equation and the better sli scales

GoogalyMoogaly · 27 Nov 2010 at 15:42

No, didn't try anything else.
If the PCI-e lane being 8x instead of 16x isn't causing an issue, I can just change the SLI profile for something to say to use only 1 GPU and that'd be the same as removing a card wouldn't it? (It's a bit awkward to keep removing the card)

chipps101 · 27 Nov 2010 at 15:45

yeah that is what i have been doing in testing and the other card sits twiddling its thumbs when sli is disabled through the nvidia control panel.

GoogalyMoogaly · 28 Nov 2010 at 18:24

Well, I didn't disable SLI, instead I just changed the SLI profile for a specific game (BC2) to be Single GPU. Judging by the temps that the cards hit that worked as one card didn't get higher than idling temps.
The odd thing was that in BC2 I was getting pretty much identical framerates with SLI enabled and disabled!
Slightly worrying/annoying...

straxusii · 28 Nov 2010 at 18:27

Trouble is you cant run one piece of software to work out where your bottlenecks are.

I suggest you run a few games whilst monitoring your cpu usage (task manager is fine)

Cleeecooo · 28 Nov 2010 at 20:07

Why don't you upgrade to C2Q - it's the same socket. Otherwise just overclock as much as you can

Scougar · 29 Nov 2010 at 09:44

GoogalyMoogaly said:
Well, I didn't disable SLI, instead I just changed the SLI profile for a specific game (BC2) to be Single GPU. Judging by the temps that the cards hit that worked as one card didn't get higher than idling temps.
The odd thing was that in BC2 I was getting pretty much identical framerates with SLI enabled and disabled!
Slightly worrying/annoying...

Don't have Vsync on do you?

allday247 · 29 Nov 2010 at 10:36

9 more posts to go aaron!

GoogalyMoogaly · 29 Nov 2010 at 10:59

Scougar said:
Don't have Vsync on do you?

I do.
The Average framerate in both cases though was around 42, so I don't think Vsync was limiting it (well, it's not like it was 60 on both, put it that way).

Maybe I need to check the CPU usage while playing (as suggested), maybe the CPU is limiting it in both cases.

eddie86 · 30 Nov 2010 at 21:26

Easiest way to find out is to record your FPS then overclock your GPUs a touch, if there is no increase in FPS then the CPU is bottlenecking. You can confirm by overclocking your CPU a bit and seeing if there is an increase.

Overclocking the GPUs a bit with Rivatuner would be the easiest, no need to worry about voltages etc if you are only increasing the speed an bit and it will give you your answer....

chipps101 · 30 Nov 2010 at 21:37

GoogalyMoogaly said:
Well, I didn't disable SLI, instead I just changed the SLI profile for a specific game (BC2) to be Single GPU. Judging by the temps that the cards hit that worked as one card didn't get higher than idling temps.
The odd thing was that in BC2 I was getting pretty much identical framerates with SLI enabled and disabled!
Slightly worrying/annoying...

bad company 2 will be cpu limited with your cpu, what gfx settings are you running it on ?

run it at as high as possible gfx settings, try running hwinfo while running the game windowed and it will show you the loads on each gpu and use core temp or task manager to monitor the cpu.