[mythtv-users] FYI - HDPVR in a KVM VM possible using usbip service

[Raymond Wagner]

On 10/9/2011 19:13, Matt Mossholder wrote:
>       Then I ran across the usbip package available in Ubuntu Natty
> (unsure on other releases, and unable to locate it for Fedora in a
> quick search). This package lets you specify a USB device to share on
> one system, and attach it to a virtual USB controller on another.

USB is designed for 1.5 microseconds of latency from one device to the 
next.  It allows for devices to be seven deep using daisy-chained hubs, 
meaning the host should expect a response from any device in around 10 
microseconds.  If you spend a couple thousand on Infiniband or Myranet 
hardware, you can achieve those low latencies.  If you're communicating 
across a physical network segment using a custom communications protocol 
on raw ethernet frames, you can get close.

If you're using standard IP protocol, which something named "usbip" 
almost certainly is, you're looking at hundreds of microseconds 
minimum.  That may be fine for a peripheral like a mouse or keyboard.  
For something like a tuner or video capture device, with limited cache 
and real communication deadline needs, it will work much less well.  If 
your host machine can run usbip, then clearly it is running Linux.  Why 
not just run MythTV on the host?

> Not bad for something so crazy :)

I'm sure the LinuxTV devs who hang around here and have had the pleasure 
of trying to write USB capture drivers can tell you just how crazy it is 
to try to use USB devices in a VM.