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Re: [Xen-devel] USB passthrough burning 5% of CPU?

On Mon, Aug 5, 2013 at 1:28 PM, Gordan Bobic <gordan@xxxxxxxxxx> wrote:
> Ever since I switched from passing a PCI USB controller
> through to a domU in favour of passing USB devices using
> the "usbdevice" config parameter, the domU affected
> seems to have qemu-dm "idling" at about 5% CPU usage in
> dom0. With the PCI USB controller passed through, this
> does not happen.
> Is this normal/expected? Does a similar continuous CPU
> overhead invisibly apply to PCI passthrough devices as
> well? Or is this CPU tax only applicable to USB
> passthrough?

Do you have the emulated USB controller enabled when you're passing
through the PCI USB controller?

My understanding was that certain USB devices must, by specification,
be polled something like a hundred times per second.  QEMU has to
emulate every one of these.  One of the things XenServer does for
really high-density VDI deployments, I believe, is disable USB in the
guests entirely.

Felipe, any comments?


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