Re: [Qemu-devel] usb slowness again (was: testing qemu svn r5890 on FreeBSD - virtio, and a patch enabling -clock dynticks)

[andrzej zaborowski]

2008/12/6 Juergen Lock <address@hidden>:
> On Sat, Dec 06, 2008 at 11:09:06PM +0100, Juergen Lock wrote:
>> Hi!
>>
>>  Jung-uk Kim sent me a patch to enable -clock dynticks on FreeBSD hosts
>> (the configure check is mine, only FreeBSD >= 7.x has posix timers that
>> this uses), I'll append it below.
>>
>>  This is the experimental qemu-devel port update I used:
>>       http://people.freebsd.org/~nox/qemu/qemu-devel-20081206.patch
>> As already mentioned I had to add a missing `#include <sys/uio.h>'
>> (files/patch-qemu-common.h), as also posted here:
>>       http://lists.gnu.org/archive/html/qemu-devel/2008-12/msg00216.html
>>
>>  I only had one (type of) guest that actually had virtio drivers (three
>> versions of sidux isos), and the speed difference between virtio-blk and
>> scsi was small.  (I tested dd bs=64k count=500 </dev/vda >/dev/null and
>> similar with a raw image, both scsi and virtio were always faster than ide.)
>> I noted tho that even virtio there was not half as fast as ide (and scsi)
>> on KNOPPIX_V5.3.1DVD-2008-03-26-EN.iso, so either overhead has increased
>> greatly from 2.6.24.4 to 2.6.26, or this has something to do with
>> the sidux kernel using CONFIG_NO_HZ and the Knoppix one (apparently) not
>> and qemu (possibly, I also suspected that with the usb slowness) not
>> handling CONFIG_NO_HZ guests too well.  [...]
>
> Well I just tried -usb -usbdevice net:vlan=1 -net user,vlan=1 with the
> Knoppix iso and got the same thruput (< 40 K/s) for wget on a local
> file than I got with sidux.  So its probably not CONFIG_NO_HZ, at least
> not the usb slowness.

I'm wondering if it's worth reverting the USB overhaul patches until
someone finds time to investigate it.  From my point of view it makes
usb emulation hardly usable, but there are also improvements brought
by these patches (mainly with passthrough).

Cheers