Re: troubleshooting I/O performance bottleneck

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Tue, Apr 28, 2009 at 08:13:36AM -0400, Thor Lancelot Simon wrote:
> On Tue, Apr 28, 2009 at 01:26:01PM +0200, Manuel Bouyer wrote:
> > 
> > This is also what I get on my test box. iostat -x shows that the vnd0
> > device is getting write requests of 32k (this is expected as the
> > xbd interface can't do 64k transfers so MAXPHYS is set to 32k for domUs),
> > and writes are forwarded to the disk as a stream of 32k requests.
> > When the write is done from dom0 the disk gets a stream of 64k requests.
> > This would explain the slowdown.
> 
> Why isn't xbdback already aggregating these requests?

I don't know; maybe because they don't come in order or something like
that ?

-- 
Manuel Bouyer, LIP6, Universite Paris VI.           
Manuel.Bouyer%lip6.fr@localhost
     NetBSD: 26 ans d'experience feront toujours la difference
--