Re: pvUSB backend performance

[Juergen Gross <jgross@suse.com>]

On 06/24/2015 03:57 PM, Konrad Rzeszutek Wilk wrote:
> On Wed, Jun 24, 2015 at 02:06:02PM +0200, Juergen Gross wrote:
>> Hi,
>>
>> my qemu integrated pvUSB backend is now running stable enough to do
>> some basic performance measurements. I've passed a memory-stick with
>> about 90MB of data on it to a pv-domU. Then I read all the data on
>> it with tar and looked how long this would take (elapsed time):
>>
>> in dom0:                     5.2s
>> in domU with kernel backend: 6.1s
>> in domU with qemu backend:   8.2s
>>
>> So the qemu backend is about 30% slower than the kernel backend. Is
>> this acceptable?
>
> That sounds about right. I remember seeing (two years ago?) an demonstration
> by kraxel where he was doing USB camera in a guest. He pointed out
> that USB1 (which is default one in QEMU) implementation sucks as QEMU
> has to poll for the commands every time. The XHCI implementation is
> better as it has some better API, or such (-EFORGOT).
>
> Oh, this has more details:
> https://www.kraxel.org/blog/2014/03/qemu-and-usb-tablet-cpu-consumtion/

This should be no problem in my case. I'm using libusb, so there is no
host adapter emulation active in qemu.


Juergen