QEMU USB performance problem

[grahams1]

Firstly I'd like to thank everyone who's made qemu such a great vm solution. I've been running a XP under Ubuntu 6.0.6 for things like netmeeting access and it work very well.

I recently tried using usb devices and I have it working but it is very, very slow. I wonder if this is to be expected with the current QEMU release 0.8.2 or am I doing something wrong.

Here is my setup

6.0.6 with a 2.6.15-26 kernel
qemu 0.8.2 with kqemu installed
Compaq n610c laptop
winxpsp2 guest
USB devices - Muvo MP3 player, Garmin Map60C GPS

starting qemu with -usb I can ctrl, alt, 2 and see the devices connected to the host with info usbhost. When I add the devices (usb_add host:xxxx:yyyy), the winxp guest can see them and detects the new hardward, all good so far.
When the usb device is being accessed the guest slows down dramatically taking hours rather thans minutes to add the device or then to access it. At the same time qemu CPU usage drops for ~80% to <1% on the host. If I turn off or disconnect the USB device the guest returns to normal performance. Interestingly the clock on the guest is now significantly out of sync with the host as though only minutes passed for the guest, when hours of real time passed.

The same happens with a MP3 player or a Garmin GPS. For the MP3 the easy fix is to tell qemu to see it as a disk drive using -hdc /dev/sda2 etc. but I have no alternative for the Garmin GPS.

Is there something I've missed or is this currently expected with 0.8.2?

[dignome]

i/o operations on host usb devices is synchronous at the moment. This means read/write ops block the execution of other code in qemu until data/status event arrives. This is also the case with disk i/o which is now being worked on.

[grahams1]

Thanks for the reply.

async i/o will be very cool, but is that the cause of the slow usb performance? as accessing disks via qemu is much, much faster than accessing a usb device. If I access the same Muvo MP3 player via usb it shalls the guest, but if I access it by its host mount point (-hdc /dev/sdc1), the performance is quite good.

[dignome]

async i/o will be very cool, but is that the cause of the slow usb performance?

Yes. Blocking a single-threaded application for up to 50 milliseconds is not good! qemu could be doing something useful during that time like executing guest code.

[grahams1]

Thanks, do you know when qemu will support async i/o?

I'd imagine the performance should then be very close to vmplayer.

[russellr]

Hi,

I have exactly this problem with WinXP under QEMU 0.9.0.

As soon as the USB device is connected (a PocketPC) the emulated machine is so slow as to be unusable.

Disconnect the USB, and it's back to normal.

If I can get this to work, I can switch off my old Windows computer!!!

What's the status of this? I'll glad donate/pay for a USB feature that works.

Otherwise, I guess I've got to go evaluate and buy VMWare.

(Unfortunately, no Linux PIM will sync properly with a PocketPC, so this is the only reason I need any Windows virtual machine.)

regards,
RR

[tDeContes]

What's the status of this? I'll glad donate/pay for a USB feature that works.

me too

what about this problem ?
is there sth new, for a year ?