[Bug 196527] Terrible KVM USB passthrough performance

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=196527

heyark (kvm-usb@suremail.info) changed:

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                 CC|                            |kvm-usb@suremail.info

--- Comment #1 from heyark (kvm-usb@suremail.info) ---

I have to agree here.
In my case, I tried to use two USB devices inside a KVM VM - and failed with
both due to timeout issues.
I pass them through to the VM using kvm parameters -usb -usbdevice
host:[vendorId]:[deviceId].

They are visible inside using lsusb. But trying to access them, both cannot be
used, while there is no problem using them directly on the host machine
(current Ubuntu 16.04.3 on a Core i5 7500).

One is a HomeMatic USB-sender
(http://www.fhemwiki.de/wiki/HM-CFG-USB_USB_Konfigurations-Adapter), the other
one is a smartcard reader.
In case of the Homematic, the driver (hmland) always says:
 usb-transfer took more than 100ms (125ms), this may lead to timing problems!
And the warning is right: nothing works, nothing gets received (using the stick
outside the VM works great).

Maybe the usb passthrough works generally with less sensible devices (did not
try an USB stick or something), but obviously the performance in handling this
is so bad, that any device that needs a proper timing is not usable.

Probably USB devices at servers are rare in the professional environments where
kvm is heavily used, nonetheless this is very disappointing. It definitely
limits the use of KVM virtualization.
Probably not a good sign too, that the following page is empty:
https://www.linux-kvm.org/page/UsbPassthrough

Is there any chance this will be cared for soon? Some kind of higher priority
for handling the USB passthrough?
Thanks!

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