Re: [Embeddedxen-devel] [Xenomai-help] Running Xenomai in a virtual machine

[ROSSIER D. <Dan...@he...>]

> -----Original Message-----
> From: Gilles Chanteperdrix [mailto:gil...@xe...]
> Sent: lundi, 22. juin 2009 16:27
> To: ROSSIER Daniel
> Cc: Jan Kiszka; xen...@gn...; GERBER Patrick; embeddedxen-
> de...@li...
> Subject: Re: [Xenomai-help] Running Xenomai in a virtual machine
> 
> ROSSIER Daniel wrote:
> >> -----Original Message-----
> >> From: Jan Kiszka [mailto:jan...@si...]
> >> Sent: lundi, 22. juin 2009 15:55
> >> To: ROSSIER Daniel
> >> Cc: Johan Visser; xen...@gn...
> >> Subject: Re: [Xenomai-help] Running Xenomai in a virtual machine
> >>
> >> ROSSIER Daniel wrote:
> >>> Just going through this interesting thread, I though it might be of
> >> interest - probably not fully related to the topic, but... - to know
> >>> that we are currently working on some integration efforts of
> Xenomai
> >> on top of the XEN hypervisor in the context of the
> >>> embeddedXEN project. For the time being, it is purely devoted to
> ARM-
> >> based processors.
> >>> In case of interest, please visit:
> >> https://sourceforge.net/projects/embeddedxen. Xenomai will appear as
> a
> >> natural subtree of embeddedXEN, like xen or minios,
> >>> but currently it is not present yet. The hypervisor and miniOS
> boots
> >> up in Mainstone/QEMU and soon on a Colibri/PXA270 board. EmbeddedXEN
> is
> >> mainly devoted to integrate multiple kernels into a single binary
> image
> >> for embedded systems with the support of hard realtime (domainU-RT,
> a
> >> new kind of Xen domain).
> >>
> >> Interesting, will have a look (again). Last time I checked was two
> >> years
> >> ago when MontaVista (IIRC) announced it. Does/will this version Xen
> not
> >> suffer from the RT problems Xen upstream has, e.g. lacking
> >> preemptibility?
> >
> > Indeed, it is a major point we want to investigate; we will assess
> the overhead bound
> > to the upcall model of XEN. It is too early to make some predictions
> >
> >> And what will be the impact on Xenomai? A new sub-arch per real
> arch?
> >> Will Xenomai run stand-alone or together with a Linux kernel as on
> real
> >> silicon? In the former case, what will be the programming model,
> >> specifically regarding RT<->non-RT communication?
> >
> > We are actually working out a standalone version of Xenomai (removing
> i-pipe) keeping
> > the strict minimum of Linux functionalities in order to bootstrap a
> simple Xenomai domain (memory manager, .
> > I do not have yet a clear vision of how the RT/non-RT communication
> will look like, but probably
> > it will rely on the event channel mechanisms of XEN. Maybe Patrick
> can tell us more about that...
> 
> Maybe a stupid question: but does the Xen domain/context switch routine
> flush the cache?

Not really a stupid question: every time a MMU-context switch occurs, the flash is 
invalidated, therefore mostly each time there is a domain context switch. 
The way how it is invalidated will depend on the processor; it is badly implemented
with PXA270/Xscale where the entire cash is flushed, requiring quite a lot of latency...
We can improve it using the Fast Context Switching Extension, but never made some tests with that.


Daniel

> 
> --
>                                           Gilles