PCIe 2.0 bottleneck?

[jessterman21]

Recently bought Skyrim for $7.50 and modded the crap out of it (no ENB or SKSE, though). My friend installed the same mods, but he noticed a lot more slowdowns than me (I still get stutters in open, busy areas). He said PrecisionX was reporting 100% utilization on BUS - which I found out was PCIe bus. I installed the Afterburner Beta, which shows the same BUS reading. Skyrim peaks at 50% and it looks like those coincide with my stutters. No other game comes close to 50%.

Researched PCIe speeds, and it looks like I'm running at 2.0 as well, even though my GTX 660 and mobo support 3.0. My i3 doesn't support over 2.0, apparently? That would explain my 50% max and the stutters, since my CPU usage peaks don't coincide with my stutters.

Any thoughts? I thought PCIe 2.0 x16 was supposed to be more than enough for a midrange card

 

[gumbykid]

The slot is fine. 3.0 speeds aren't much better (if at all) at this point, there just isn't enough optimization.

As for your CPU, only the Ivy Bridge series supports PCIe 3.0.

Can you list both you and your friends full builds?

 

[CraigN]

Gumby is absolutely correct, and that's an awesome infographic there, I may have to steal that.

PCIE 3.0 is only marginally faster. Single card solutions do not saturate the PCIE 2.0 lanes. If you move into an SLI setup, that's where some benchmarks are starting to show a difference.

 

[gopher1369]

Any thoughts? I thought PCIe 2.0 x16 was supposed to be more than enough for a midrange card

That's what I thought too. The Sandybridge cards only support DDR3 1333 and PCIe 2. If you upgraded to an ivybridge Core i3 3210, which is Ivybridge, you'd get PCIe 3.0 and your memory would speed up as well as Ivybridge CPUs support DDR3 speeds of 1600, but I'm not sure how much benefit that would actually give you, if any at all.

 

[jessterman21]

The slot is fine. 3.0 speeds aren't much better (if at all) at this point, there just isn't enough optimization.

As for your CPU, only the Ivy Bridge series supports PCIe 3.0.

Can you list both you and your friends full builds?

Mine's in my sig. My friend's is i5-750 + GTX 560 Ti + 8GB DDR3-1333.

I think a modded Skyrim is a special case, since I haven't seen the BUS usage even come close to 50% in any other games I own.

 

[gumbykid]

@gopher
RAM speeds have also shown to not make a difference in most games. Only 2133mhz seems to make an impact.

@Craig
Here is the full article with a bunch more games
http://www.techpowerup.com/reviews/Intel/Ivy_Bridge_PCI-Express_Scaling/15.html

@jesster
Your friend should get around 10FPS less than you with that card, however with heavy modding that number will only increase. How different are the fps you two are getting?

 

[jessterman21]

@jesster
Your friend should get around 10FPS less than you with that card, however with heavy modding that number will only increase. How different are the fps you two are getting?

I'm getting an average of 50fps outside with >100ms stutters here and there, and he was getting 40fps with sustained drops to 20fps.

Looks like PCIe speed makes more of a difference in Skyrim than most other games, and these results are without the mods and 2K textures I'm using... From that TechPowerUp article:

 

[gumbykid]

Seems right except for the drops. Does he have all the updated drivers? Having old ones could cause the full load issue. Also, if he had poor airflow the GPU could be overheating and dropping in FPS.

There still aren't noticeable differences, except for the very first one. Even then, you are using 2.0x16, which is identical to the 3.0x16 fps.

 

[gopher1369]

@gopher
RAM speeds have also shown to not make a difference in most games. Only 2133mhz seems to make an impact.

What are you talking about? He gets a whole extra extra 1FPS.

 

[gopher1369]

Looks like PCIe speed makes more of a difference in Skyrim than most other games, and these results are without the mods and 2K textures I'm using...

I can't see any differences on there, the difference between PCIe 2 and 3 on that chart is less than 1FPS, which is within the margins of error.

Edit: actually the 7970 results actually show the PCIe 2 (75.2FPS) being faster than the PCIe 3 (74.4FPS)!

 

[jessterman21]

Okay, just tested a bunch of games, and max BUS usage was 14% when first starting the Arkham City Benchmark. Mostly it was at 3-5% for those games. I wonder if it's a certain Skyrim mod that's eating all the bandwidth.

I'm also installing an i5-3570K this weekend which will allow me to use PCIe 3.0, so I'll definitely be back with the results.

 

[gamerk316]

We barely saturate PCI-E 1.1 x16, let alone PCI-E 2.0 X16. More likely something else is causing your slowdowns.

 

[gumbykid]

The only difference you will see is the fact that youre upgrading your CPU. Do you two have identical mods?

 

[jessterman21]

@gamerk316, I believe you - none of my other games ever gets above 5% and I've never seen PCIe bandwidth being a bottleneck anywhere online, but it's the only thing we've both noticed with our particular brew of Skyrim mods.

@gumbykid, yes - I made him a CD with the ones I have installed, then he downloaded some of the texture mods I use, too.

Does anyone have experience with the Afterburner/PrecisionX reading that shows BUS%? Maybe I'm on a wild goose chase, but I'll know by Saturday whether PCIe bandwidth is the issue.

EDIT - I think I'm on the right track if vanilla Skyrim is showing PCIe 3.0 benefits in a single card:

 

[gumbykid]

I've never seen an issue with PCIe 2.0 being too slow, so I don't think that's the issue. Your friend not having the updated drivers is more likely.

What FPS are you running at? If you're running at 40 and your friend is running at 25 (due to the difference in GPUs) then it will seem like a huge difference, yet it's just because his card can't keep up.

 

[jessterman21]

Okay, doesn't look like BUS is my issue. My stutters look like they're tied to Core 0 getting near 100%. Tested at 1280x800 with no AA or AF, and then at 2160x1350 with 8xAA and 16xAF, plus Quality AO. Got the same stutters.

 

[gumbykid]

Your CPU is bottlenecking your GPU then. As it was recently pointed out to me, Skyrim runs on an engine that's not well optimized.

So your issue is CPU bottlenecking. Your friends issue is that his card isn't good enough for Skyrim with mods (the fps benchmarks are taken indoors).

 

[jessterman21]

Yep, my stutters were CPU - still there on my i5, but the length has been halved. And my friend and I may have been reading the FB (GPU memory bus) instead of BUS (PCIe bus) graph. BUS never goes above 20% and FB goes up to 55% on mine. Not sure what his issue was, but he uninstalled a bunch of texture mods and it's working better for him - told him his 1GB card couldn't handle it anyway.