scsi emulation throughput (was: Re: qemu-cvs FreeBSD guests, cirrus, vmwarevga emulation - experimental qemu-devel FreeBSD port update available for testing)

[Juergen Lock]

On Sun, Jan 06, 2008 at 11:44:50PM +0100, Juergen Lock wrote:
> Hi!
> 
>  Yesterday (so, just before the qemu version commit...) I prepared a
> FreeBSD qemu-devel port update using the 2008-01-05_05 snapshot,
> 	http://people.freebsd.org/~nox/qemu/qemu-devel-20080105.patch
> and I already got a report of xorg 7.3 using the cirrus emulation in a
> FreeBSD 6.3 RC guest crashing with -kernel-kqemu, and hanging without it,
> which he said worked with the previous qemu cvs snapshot thats still in
> ports (2007-08-02_05.)  -vmwarevga worked, but still had the old problem
> of causing the ne2kpci nic not to attach (ed0.)  The i82557b nic can be
> used as a workaround (fxp0, its faster anyway), but I just verified with a
> FreeBSD 6.2 guest (you can use e.g. a FreeSBIE livecd iso, use `su' if
> you want to edit its /etc/X11/xorg.conf, after that exit the root shell
> and run `startx'; I gave qemu -m 256) that -vmwarevga also still causes
> the es1370 soundcard not to attach and I don't know a workaround for
> that.  Also, still slirp causes qemu to crash on amd64 hosts when just
> trying to access a webpage from inside a guest.
> 
>  So, can anyone reproduce any of these problems on e.g. a Linux host?
> Also, more testing of the FreeBSD port update is certainly needed, also
> using non-FreeBSD guests, non-i386/amd64 targets, and the new -disk option

(...which is now called -drive btw.)

> (which I didn't yet test at all, it should e.g. allow scsi drives to be
> emulated, tho very likely FreeBSD host support for the scsi passthru
> feature still needs to be done, and io via qemu is probably too slow to
> burn a dvd anyway. :)

 Actually...  I just played with -drive if=scsi and -kernel-kqemu in a
linux guest and a dd bs=64k from a 5MB file to /dev/null got me more
than 25 MB/s!  While a similar dd off the emulated ide cdrom drive (I was
using a livecd iso, sidux-2007-04.5-200712260120-eros_xmas-kde-lite-i386.iso)
only gets me about a tenth of that.  Can anyone reproduce this? :)  This is
the first time I've seen qemu doing more than a few MB/s IO on this box...

 Btw a FreeBSD (FreeSBIE) guest didn't get nearly as much, tho that may
partly be because the image I used was vfat and FreeBSD's msdosfs
is not exactly fast.  (Or maybe scsi tags weren't enabled or something.)

 Still surprised...
	Juergen