Re: Poor write- and overall performance

[Ryan Harper <ryanh@us.ibm.com>]

* Arne Kepp <ak@opengeo.org> [2008-12-19 19:45]:
> Avi Kivity wrote:
> >Arne Kepp wrote:
> >>Hi,
> >>
> >>I'm testing KVM 80 (prepackaged from lfarkas.org) on CentOS 5.2 (both 
> >>guest and host) and comparing against Xen 3.3.0. The only 
> >>modification I've really made is that I've set noatime on both guest 
> >>and host. The guest is running straight from an LVM volume and is 
> >>assigned 4 Gb RAM and 4 virtual CPUs.
> >
> >I suggest trying scsi in kvm-81, or setting cache=writeback if you 
> >want to keep using IDE (but be aware of the potential for severe data 
> >loss with the latter option).
> >
> 
> Thanks for the tip. I tested with the SCSI driver and 81, unfortunately 
> write performance was approximately the same as before.

Yeah, currently the scsi emulation doesn't queue up writes, rather it
waits for each one to complete which means one cannot take advantage of
the aio infrastructure.  I'm currently working on fixing this; stay tuned.

-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
ryanh@us.ibm.com