Unexplained CPU usage when fourth camera is added

[Robert Swackhamer]

We just recently put together some new hardware based on Sandy Bridge (yes, I know about the chipset, we'll replace the motherboard later) and we ran into some odd CPU usage numbers that we can't really find an explanation for it. First, here are some tech specs:

Core i7 2600k
MSI P67A-GD55 mobo
8GB Patriot DDR3-1600 RAM (2x4GB)
EVGA GeForce 8400 GS vid card
2x MS LifeCam HD-5000
1x MS LifeCam Cinema
1x MS LifeCam Studio
Streaming to Bambuser at 1200kbps for video at 720p
VidBlaster Home 1.24

In my current setup for VB Home I have the streamer module send to FMLE so I can stream with H.264 (and yes, Sandy Bridge really does help with that). But I have two different situations that I just can't find a reason behind...

Situation 1:
CPU usage with 3 cams prior to streaming: mid-20s
CPU usage with 3 cams while streaming: mid-70s

Situation 2:
CPU usage with 4 cams prior to streaming: bounces between mid-20s to low-30s
CPU usage with 4 cams while streaming: mid-90s

I was expecting a bit more linear scaling of CPU usage with the fourth camera on, but this isn't the case. I do have the fourth camera on a seperate USB controller that goes through the PCI slot, and switching cameras between controllers didn't seem to introduce any changes.

I'm really baffled by this one since the change in numbers doesn't make any sense to me. Any ideas?

[Mike]

First of all, if you do not publish the number with 1 and 2 cameras there is no way we can see that this does not "properly scale", the numbers look quite normal to me. Second, there is no such thing as properly scaling as CPU usage depends on many more factors than the number of cameras. Even if you were using the exact same cameras connected in the exact same way, you can still see numbers that do not look normal simply because we've seen many driver bugs that cause unexplained stress when using more than one camera. Lastly, you really should not push your system this high and keep it at least out of the red zone.
Oh, and do a Search for "USB overload" as that is a potential problem you are facing when hooking up 4 USB cameras.

[Moved to Hardware]

[Robert Swackhamer]

I knew there was a piece of information I had forgotten to add in there. I ended up using the Camera I modules as for some reason when I tried the Camera II modules none of the webcams would show up in the available drop down list. That may be something I'll have to experiment with later.

[Robert Swackhamer]

After tearing myself away from Marvel vs. Capcom 3 this evening I sat down to do a little experimentation to see if I could figure out why the CPU usage was so high when the fourth camera was on during streaming.

I took Mike's advice and tried out the Camera II modules. Here I did run into one snag. Having three C2 modules was fine. But for some reason after adding the fourth no camera would come up regardless of which one I chose. So I ended up with three C2 modules and one C1. Running this way did yield a drop into the low 80s.

What I find so funny is that it only occurs when FMLE is actively streaming. Any other time (when when FMLE is running but not streaming), the presence of the fourth camera barley registers. Too bad there didn't seem to be a way to get FMLE to not pay attention to the USB cams and only pull from VB... maybe they're fighting over who gets to use it first.

[Amnon]

Shoot, I knew I should have written it down.
We had the same problem here Saturday. But what was different is that a cam that was working all along stopped working. The CPU usage was in the 90's. TaskManager showed a file up there that I cannot remember the name of anymore, but it was just a munch of letters, which was using almost 40%. Mike did a search on it and found that it may be a problem with hardware. I was going to replace the USB card and see, but decided to first just connect a good cam to the bad port. So I swapped two cables and all cams came up, and that mysterious file disapeared and usage went back to around 30%.

Look at your taskmanager, click on processes, and sort by cpu usage. If you something that is using unusually high percentage of cpu and you don't know what it is, email it to me, and I am sure I will recognize it if it was it.

[Robert Swackhamer]

Look at your taskmanager, click on processes, and sort by cpu usage. If you something that is using unusually high percentage of cpu and you don't know what it is, email it to me, and I am sure I will recognize it if it was it.

I tried that out and unfortunately it's VidBlaster and FMLE taking up the CPU time, and the math did add up with what I was seeing, so there's no hidden processes going on during this time.