[Xen-devel] Re: poor domU VBD performance.

[peter bier <peter_bier@xxxxxx>]

CÃdric Schieli <cedric <at> schieli.dyndns.org> writes:

> 
> I've just tried with latest testing tree DomO and DomU and got same
> results.
> 
> Le samedi 02 avril 2005 Ã 00:22 +0100, Ian Pratt a Ãcrit :
> >  There have been some changes to the frontend driver too: you might want to
try using the 2.0-testing kernel
> in domU too.
> > 
> > Also, a really nasty CPU performance bug got fixed earlier this evening, so
you should make sure you have
> the latest tree.
> > 
> > Ian
> > 
> > > > I just ran again, and for some reason it looks fine now...  
> > > I have no 
> > > > idea what I did to get the lower numbers initially, perhaps an 
> > > > inadvertant IO scheduler change.  Service commit times are 
> > > .28ms and I 
> > > > can drive ~58MB/sec with just 16k requests on xen0.  I'll 
> > > do some more 
> > > > tests to get a more consistent picture.
> > > > 
> > > 
> > > I still experience bad performance in domU with latest 
> > > xen-testing dom0.
> > > 
> > > Here's my setup :
> > > 
> > > Xen : 2.0.5
> > > Dom0 : 2.6.11-xen-testing (20050401 ~22h CEST) running Debian 
> > > Sarge DomU : 2.6.10-xen-2.0.5 (8G LVM backed VBDs exported as 
> > > hda1) running Gentoo Processor : AthlonXP 1800+ Chipset : VIA 
> > > KT600 Drive : Seagate ST380013AS 80G SATA
> > > 
> > > And my results :
> > > 
> > > Dom0 : 51 MB/s
> > > DomU : 36 MB/s
> > > 
> > > I've tried with request sizes from 128k to 1024k reading 
> > > entire volume and obtained always same results.
> > > Changing the scheduler on Dom0 and/or DomU doesn't change anything.
> > > 
> > > I can give you more info if nedded.
> > > 
> > > --
> > > CÃdric Schieli
> > > 
> > > _______________________________________________
> > > Xen-devel mailing list
> > > Xen-devel <at> lists.xensource.com
> > > http://lists.xensource.com/xen-devel
> > > 
> > 
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel <at> lists.xensource.com
> > http://lists.xensource.com/xen-devel
> 


It just sumbled accross the fact, that you are using a SATA disk, CÃdric. This
is 
exactly the "dd" behavior that  my system containing SATA disks still shows. 
But 
it
applies only to "dd" ( which, admittedly is read-only ). It does not apply to 
the performance figures I got when copying my "/usr" tree - as described in a 
previous post here - from one location of the disk to another location on the
same disk ( which, of course is combined read-write on the same device ). Hence
it might be possible that my limited performance copying from one disk to
another might in fact be an effect of reduced read performance in DomU on a 
SATA disk.  

I suspect that this might be an effect specific to SATA disks. I will verify 
this on monday - when I have access to my computers in the office, by doing it
on a system with two IDE disks. I will report it then, if your problem is still
open. 

I will describe the exact configuration of the systems then (Motherboard, IO 
Controller, etc ).


Peter 


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