Re: [Xen-devel] Xen & I/O in clusters - problems! New Information

["Mark A. Williamson" <mark.williamson@xxxxxxxxxxxx>]

Domain 0 is (from the POV of Xen) basically Just Another VM and is scheduled 
pre-emptively.  Some capability flags give the Dom0 VM the privileges it 
needs in order to control devices, screen, Xen management functions etc.  If 
you use the buggy Atropos then you'll lose performance even with just one 
domain.

HTH,
Mark

On Thursday 28 October 2004 11:51, Hïvard Bjerke wrote:
> We're getting these results in domain 0, not in a VM. As I understand, BVT
> or apropos scheduling do not apply in domain 0?
>
> HÃvard
>
> On Wed, Oct 27, 2004 at 07:40:27PM +0100, Mark A. Williamson wrote:
> > Just a thought: you are using the BVT scheduler, right?  We haven't
> > tested performance with the other schedulers recently but we know
> > something goes wrong for IO intensive domains on Atropos.
> >
> > Mark
> >
> > On Wednesday 27 Oct 2004 19:26, Ian Pratt wrote:
> > > > On Fri, Oct 22, 2004 at 06:47:35PM +0100, Ian Pratt wrote:
> > > > > > We tried to compile xen0 with CONFIG_E1000_NAPI = y and got the
> > > > > > samre results between
> > > > > > two xen dom0 nodes. I am not sure if these interrupts tells
> > > > > > anything:
> > > > >
> > > > > It's the different rate at which the eth0 interrupt counts go up
> > > > > during your bandwidth tests that is interesting. e.g. poll it
> > > > > once a second during the test.
> > > >
> > > > We tried sending 1 MB and measured:
> > >
> > > 1MB isn't really very much with a 128KB socket buffer. Do you get
> > > the same results with larger transfers?
> > >
> > > > non-SMP native Linux:
> > > >  ~ 130k interrupts
> > > >  114 kB/s
> > > > native Linux with compiled-in SMP support, single CPU:
> > > >         ~ 140k interrupts
> > > >         114 kB/s
> > > > Xen0:
> > > >         ~ 180k interrupts
> > > >         80 kB/s
> > >
> > > It's pretty odd that Xen's taking more interrupts. Are you using
> > > the same native kernel version as you are for Xen?
> > >
> > > Also, what happens if you boot xen with 'nosmp' on the Xen
> > > command line.
> > >
> > > We've got Xen tcp performance results from a bunch of machines,
> > > and dom0 to dom0 performance has always been almost identical to
> > > native for 1500 byte MTU packets.
> > >
> > >
> > > Ian
> > >
> > >
> > >
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