2600k and sandybridge finally starting to run out of steam in SLI

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Aaron_ATX

[H]ard|Gawd
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Oct 15, 2003
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Been running a sandybridge 2600k since about the time they were launched, and I believe I am starting to see the end of its capabilities....

Just added another 780ti sc and have been messing with surround displays at 3240x1920, and just not getting the performance out of the setup I think I should be.

Intermittent stuttering while benchmarking in SLI and poor framerates in newer games have got me taking a close look at my monitoring software, and I think I have figured out what the hell is going on.....

Using nvidia surround, all connected correctly @ 3240x1920 I was getting low gpu usage numbers and low power consumption, that all corresponded with bus usage hitting 90 to 99%

Spikes to 98%, framerate drops because of the pci-e 2.0 bandwidth bottleneck at that resolution, games play like crap because of the cards throttling to 50-60% power and usages all over the place.


So I decided to switch back to single monitor 1920x1080 gaming and instantly the bus usage went waaaaay back down to around 30-50%, frame rates shot through the roof and the stuttering is gone.

Durrr, I suppose.


But now, with both cards able to operate at capacity, my poor old 2600k @ 4.6 is loaded up at around 80-90 percent. Still games fine, but I am seeing the end of the road here, I think.


So i'm going to spend some cash on an upgrade... really got to liking the 3240x1920 surround, but that appears to be a little more than my rig can drive to my liking...

would like to go single monitor 1440, but I am wondering if I am going to run into pci-e 2.0 limitations and run out of juice on my cpu at the same time.

Do I have to stick it out at 1920x1080 for now and upgrade my mobo/cpu? Or can I treat myself to a 1440?

Opinions / thoughts wanted!
 
cpu bottlenecks play more of a role at low resolutions than high. Usually the higher the rez the higher the gpu load and cpu load stays the same. I'm wondering if the mobo dropping your cards to 8x / 8x in SLI is more likely the real culprit.

Honestly I ran 2 290s @ 5760x1200 with my 2550k @ 4.8 and no problems. I recently upgraded to the 4790k and got a decent boost in benchmarks but haven't seen any massive improvements in gaming. If you get in on a good microcenter sale I say go for it. You can sell off your current stuff to nearly pay for the upgrade. If you have to purchase things at full price I think I would wait for next gen stuff to drop.
 
Could there be something else going on on your system that might explain the performance drop? Most of the in-depth reviews that I've read have stated that there is not much difference between PCIe 2.0 x8/x8 and PCIe 3.0 x8/x8 performance. Here is one such example: http://www.techpowerup.com/reviews/NVIDIA/GTX_980_PCI-Express_Scaling/22.html

What motherboard are you running? Are you sure that it is running in x8/x8 mode with dual-GPUs? Technically it should be, in order to be SLI certified, if I recall correctly, but there have certainly been shenanigans on the part of motherboard manufacturers in the past. Also, is it possible that a performance discrepancy between the two cards might factor into the poor performance?

I have not run SLI on any of my machines since I had my SLI GTX 480s, but I've worked on quite a few with beefier video cards in SLI (670s, 680s, 970s) that were running Sandy Bridge CPUs. I never noticed a setup where the CPU was the limiting factor, even in surround-mode. The 2GB VRAM limit on older cards certainly manifests itself, but appropriate settings tweaks generally fixed that.
 
Sounds like more of a PCIe limitation than the actual CPU cores running out of steam. Shame really, since the PCIe controller is on the CPU itself.
 
Sounds like your GPUs are probably being starved for bandwidth trying to feed the 3240x1980 surround setup through a PCIe 2.0 interface. Have you verified x8 + x8 2.0 mode or do you have one of your GPUs installed in PCIe x16_3 (black colored slot)?
 
MrCaffeineX said:
/snip Could there be something else going on on your system that might explain the performance drop? /snip

I've checked and double checked, nothing so far. I removed my Xonar PCI soundcard as well just to make sure. Also checked what I/O's are being shared with the gpu's and nothing strikes me as being alarming

What motherboard are you running? Are you sure that it is running in x8/x8 mode with dual-GPUs? /snip

ASUS P8P67PRO rev 3.1. Have the BIOS option for the other 2 pci slots on the board set to x1 as that apparently is supposed to let the main slots run at x8

GPU-Z verifies with full screen rendering mode that both cards show as PCIe2.0 x16 @ x8 when running


Also, is it possible that a performance discrepancy between the two cards might factor into the poor performance?

Cards are identical EVGA 780ti SC. I've tried just running with no overclock, and mild overclocks, seems to make no difference

/snip I never noticed a setup where the CPU was the limiting factor, even in surround-mode. The 2GB VRAM limit on older cards certainly manifests itself, but appropriate settings tweaks generally fixed that.

CPU isn't a limiting factor (or getting close at least) until I run in single monitor, performance mode at 1920 x 1080 ...because then I get full GPU usage. Trying to run surround @ 3240 x 1920 the CPU just coasts along because, according to my monitoring software my pcie bus spikes to 99%
Click to expand...


haste. said:
What's your PSU?
Click to expand...

PSU is an AX860 Corsair. Just picked up a kill-a-watt today to make sure im not totally pegging my psu out. Havent tested that yet.



DejaWiz said:
Sounds like your GPUs are probably being starved for bandwidth trying to feed the 3240x1980 surround setup through a PCIe 2.0 interface. Have you verified x8 + x8 2.0 mode or do you have one of your GPUs installed in PCIe x16_3 (black colored slot)?
Click to expand...

That was the feeling I was getting, but again I have never run into a problem like this before. I am running all 3 monitors off one (the top most) 780ti. 2 dvi and one display port. That supposedly is acceptable..... I picked up another dual link dvi today to try and split the monitor connections between cards.

GPU's are in the blue and while slots.

Thank you for the feedback so far!
 
3240x1920 is less than 4K resolution (3840x2160). I went looking for some 4K SLI reviews that were using Sandy/Ivy Bridge CPUs (not the x79 variants), but I'm not finding a hell of a lot of those out there, especially in English. I would have thought that dual PCIe 2.0 x8 should have provided enough bandwidth for 4K, but maybe it isn't.
 
I just ran a few tests with my 780 Ti OC at 1440p with a 2600k at 4.5 ghz..

Single card, single 1440p screen. I ran a few different games, GPU at 100% in every game and CPU between 20-40% in every instance.

Makes no sense at higher resolution you'd get more CPU and less GPU usage. Try different games, could be a surround issue. Could be an incorrect PCIe bus setting in the bios, could be a bad 2nd card. SLi bridge not right, 2nd card not getting the power it needs from the PSU (did you hook power up right, wouldn't hurt to check).

Dont just go spend all the cash to upgrade without messing around with it first...I quick google search for pcie 3.0 vs 2.0 shows virtually no difference in performance.
 
Theoretically, an x8 PCIe 2.0 slot should provide plenty of bandwidth for a 780ti and there should be negligible performance differences compared to a x8 (or even x4) PCIe 3.0 slot, even at higher resolutions and graphics settings.

A lot of reviews out there regarding PCIe revision and link speed for 600, 700, and 900 series cards, but I can't find a single one that addresses/includes SLI performance amongst the various slot revisions and link speeds with a plethora of resolutions and graphics settings...

4 GB/s = PCIe 2.0 x8
...same as PCIe 3.0 x4

8 GB/s = PCIe 2.0 x16
...same as PCIe 3.0 x8

Again, either link speed should be plenty for a pair of 780ti's. Make sure you've gone through everything to ensure that they are operating at 2.0 x8 mode and SLI is turned on; not just at the global level, but in the specific game profile within the NCP, as well.

If you aren't using Adaptive Vsync, you may want to enable it.
 
I did notice that when switching from surround to single display, I have an option with each game profile for "SLI rendering mode" ..... when using surround that option does not exist.

I'm wondering if this has something to do with the "Maximize 3D performance" vs "Span displays with surround" options in NCP. When running surround, the maximize option would only allow me to run the main (center) display, (1920x1080) and would drop signal to the others. Only way I could get 3240 x 1920 to operate in games was to use the span displays with surround instead.
 
Just ran a pass of haven 4.0 @ 1920x1080 in SLI, saw a max of 670-680 watts at the plug. Thats with both cards at max powerthreshold of 106, max gpu voltage on both was 1.212 and steady. Only a slight overclock on both cards, max boost it saw was 1162. Didnt monitor cpu core load but I know haven isnt too tough on my cpu
 
It's time to upgrade. I used to have a 2500k and 2600k and saw a pretty big difference going to a 4930k. Those 2500k/2600k are still great cpu, but your part of one of the instances where they will bottleneck your setup with pcie 2.0 (sli+surround). The Time for pcie 3.0 has come. You technically would be ok at 1440p but then you'll have DSR available which is an amazing thing to use if you have the extra hp (you do)
 
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Aaron_ATX said:
PSU is an AX860 Corsair. Just picked up a kill-a-watt today to make sure im not totally pegging my psu out. Havent tested that yet.
Click to expand...

I would think 860w would be plenty, unless the PSU has been abused.

I'd be curious to see where you are at in power consumption. 2 x 780ti maxxed can use around 500w, add on the 2600k with extra voltage, the mobo and periphs... maybe an extra 200-250w.

I'm guessing you monitored the temps to make sure that nothing is thermal throttling?
 
Honestly I'd be looking elsewhere to solve the stuttering, if you can hit 4.4Ghz+ on your chip - it should pretty much saturate anything. I just replaced a faulty HDD that was causing stutters in games, fps drops and usage spikes, and switched to an ssd gamedrive.
 
Ahh, very nice. That seems to agree with what I am running into. Going to go back through all my chipset drivers, use only dvi-d connections (was using one displayport) and anything else I can think of before I pull the trigger on a new mobo/cpu combo. Thank you for pointing that thread out. I had missed it.

Quite impressive really just how long a sandybridge system can go.
 
I know this is an old thread but thought I would add my two cents. Was running a I7 920 with SLI 970's in an ASUS ROG RAMPAGE II that runs PCI-e 2.0 X16 for both cards then switched to ASUS x-99a that runs PCI-e 3.0 x16/x8 in SLI (which is the same speed as PCI-e 2.0 @ 16x). Performance from stuttering was night and day. Some games where unplayable until I upgraded CPU. The old "I checked CPU usage while in game" was nonsense. The 920 would be at 50% across all cores so I thought I was not CPU bottlenecked.
 
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