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

[Juergen Lock]

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.

 Just thought I'd mention...
	Juergen