CPU usage 100% = bottleneck?

[Skuzzy]

If the power draw from the USB ports comes close to the limits of the built-in hubs, then a brown-out condition can occur where the USB hub sends millions of interrupts to the CPU causing a heavy spike in CPU usage.

In Windows 7, it was a critical condition which could cause the system to crash.  In Windows 8, and later, Microsoft instituted a hack/fix, of sorts, which shuts down the USB hubs ability to generate an interrupt and then they switch to polling mode.  It is less efficient and uses more CPU time, but it keeps the system from crashing.

To my knowledge, there has never been a motherboard which had full support for the power draw limits specified for the USB bus.


Oh Bizman, my early response about the older chip sets was more of an FYI thing that may or may not have anything to do with the system in question.

[Bizman]

Oh Bizman, my early response about the older chip sets was more of an FYI thing that may or may not have anything to do with the system in question.

Thought so. 

[FESS67]

Atlau, are you using any powered usb hubs or is everything straight into the PC?  Often a powered hub is useful.  I have an 8 port powered hub that handles my trackir, pedals, stick, throttle and some other peripherals leaving the pc ports for yhe vr sensors and headset.

[atlau]

Everything is plugged into my computer directly. Mouse, keyboard, printer, usb wifi, throttle, joystick, vr headset. Is that too many?

[The Fugitive]

Everything is plugged into my computer directly. Mouse, keyboard, printer, usb wifi, throttle, joystick, vr headset. Is that too many?

That could be. The power for all those comes from your power supply. If you dont have a robust one in your computer it may give you trouble. Powered USB hubs dont have the greatest power supplies, but it does take some of the load off of the computers power supply.

In my case, flight controls are all on one USB hub, peripherals on a second, and VR stuff on the computer.

[Bizman]

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In my case, flight controls are all on one USB hub, peripherals on a second, and VR stuff on the computer.

That sounds like a perfect solution since a desktop usually has a few USB lines. Spreading the load to all of them and adding extra power seems more reasonable than using just one mega hub.

[Skuzzy]

That could be. The power for all those comes from your power supply. If you dont have a robust one in your computer it may give you trouble. Powered USB hubs dont have the greatest power supplies, but it does take some of the load off of the computers power supply.

In my case, flight controls are all on one USB hub, peripherals on a second, and VR stuff on the computer.

The amount of power which can be supplied to the USB peripheral is not regulated by the power supply of the computer.  It is regulated by how much current the USB chipset can allow.  While the specification for USB 1.x and 2.x allows for a maximum of 500mA, and 900mA for USB 3.x, the amount of current is usually far from that in the actual implementation.

The maximum per connected USB device was set at 100mA for USB 1.x and 2.x, and 150mA for USB 3.x.  In reality there have been many devices which violated that current draw.


A computer has X number of USB hubs in it, with Y number of USB ports attached to each hub.  No manufacturer, I am aware of, has ever put external labeling on the ports to tell you which hub they may be connected to leading to easily overloading any give hub.