Re: Poor network performance with cable modem assigned to guest

[Jon Fairbairn <jon.fairbairn@cl.cam.ac.uk>]

Jim Paris <jim@jtan.com> writes:

> Jon Fairbairn wrote:
>> Brian Jackson <iggy@theiggy.com> writes:
>> 
>> > On Friday 28 August 2009 01:14:42 pm Jon Fairbairn wrote:
>> >> The setup was done through virt-manager. The network between the host
>> >> and guest is a virtual bridge. What I've been trying to do is to assign
>> >> a USB cable modem to the guest,
>> >
>> >
>> > This is probably your problem here. KVM only emulates a usb1.1
>> > controller,
>> 
>> that shouldn't be a problem as the cable modem is only a usb 1.1 device.
>> 
>> > and from all reports, it doesn't really do that very well.
>> 
>> Not very well? We're talking about a factor of *FIFTY* slow down here.
>> If I'd implemented the driver in a 1980s lazy functional language I
>> would have only expected a factor of ten :-P ;-).

> I don't have any specific answers, but you might be able to get some
> more info by uncomenting the "//#define DEBUG" in kvm's usb-linux.c.
> You might also try capturing the USB traffic (e.g. with wireshark)

Thanks for your comments; I was waiting for a time when the network
wasn't in constant use to try some experiminents, but unfortunately my
ISP has replaced the cable modem with a newer version that doesn't have
a USB port, so I have to abandon this approach anyway.

[Assigning a physical PCI device to a kvm guest doesn't work with 
AMD Athlon(tm) 64 X2 Dual Core Processor 4400+
does it?]

-- 
Jón Fairbairn                                 Jon.Fairbairn@cl.cam.ac.uk