Re: Disk performance hit with Dom0 vs native?

[Florian Heigl <floh%deranfangvomen.de@localhost>]

Hi Stephen,

On Thu, Nov 17, 2005 at 03:07:38PM +0000, Stephen Borrill wrote:
> With an IBM x206 and 3.0_BETA as of about a week ago, I see a very big
> difference in apparent disk write performance between dom0 and booting 
> from a GENERIC kernel.
> 
> Using "dd if=/dev/zero of=/dev/rwd1d bs=1m", I get about 11MB/s under Xen, 
> but 59MB/s with GENERIC. Is such a difference to be expected?
 
this is far more than I'd expect from my experience:

NetBSD xen-host-2 3.0_BETA NetBSD 3.0_BETA (XEN0) #0: Sat Aug 13 13:50:25 UTC 
2005  
builds%works.netbsd.org@localhost:/home/builds/ab/netbsd-3/i386/200508120000Z-obj/home/builds/ab/netbsd-3/src/sys/arch/i386/compile/XEN0
 i386


xen-host-2# dd if=/dev/zero of=lala bs=1024k count=1024
1024+0 records in
1024+0 records out
1073741824 bytes transferred in 19.658 secs (54621112 bytes/sec)

on my domUs (which live on a smaller and slower disk and also of course
experience some overhead) I get approx 13MB/s.

I can't guess on a good reason for what You experience, though. :/

Rgds,
Florian

--
florian heigl                    http://deranfangvomen.de/

Grid Computing erfreut sich gerade bei Windows-Nutzern sehr regem Zuspruch, auch
wenn die Rechnerbesitzer meist nichts von ihrem Glück wissen. --f. weimer