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Depends what Xen services you want to use. :-)

If you run a RTOS with its own device drivers on its own CPU (not
sharing with anyone else) then you will probably find that Xen adds
very little jitter already.

If you want to be able to use services in other guests (e.g., remote
device drivers) that are multiplexed, then the problem is (at least)
much much harder.

-- Keir

> Folks,
>
> I know that Xen is designed for servers and such. But defined
> latency (e.g. real time) responsiveness is one of those
> characteristics that needs to be addressed early in the development
> lifecycle. What are the team's thoughts on achieving some sort of
> latency guarantee. (No fair punting by saying that some I/O devices
> can never guarantee latency, those devices do not need to be supported
> for defined latency situations.)
>
> Andrew
>
> ____________________________________
> Andrew W. Donoho
> awd@DDG.com, PGP Key ID: 0x81D0F250
> +1 (512) 453-6652 (o), +1 (512) 750-7596 (m)
>
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Folks,

I know that Xen is designed for servers and such. But defined latency
(e.g. real time) responsiveness is one of those characteristics that
needs to be addressed early in the development lifecycle. What are the
team's thoughts on achieving some sort of latency guarantee. (No fair
punting by saying that some I/O devices can never guarantee latency,
those devices do not need to be supported for defined latency
situations.)

Andrew

____________________________________
Andrew W. Donoho
awd@DDG.com, PGP Key ID: 0x81D0F250
+1 (512) 453-6652 (o), +1 (512) 750-7596 (m)


--Apple-Mail-23--755923030
Content-Transfer-Encoding: 7bit
Content-Type: text/enriched;
charset=US-ASCII

Folks,


I know that Xen is designed for servers and such. But defined latency
(e.g. real time) responsiveness is one of those characteristics that
needs to be addressed early in the development lifecycle. What are the
team's thoughts on achieving some sort of latency guarantee. (No fair
punting by saying that some I/O devices can never guarantee latency,
those devices do not need to be supported for defined latency
situations.)


Andrew


<fontfamily><param>Helvetica</param>____________________________________

Andrew W. Donoho

awd@DDG.com, PGP Key ID: 0x81D0F250

+1 (512) 453-6652 (o), +1 (512) 750-7596 (m)


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There's a soft realtime scheduler in Xen called Atropos, which can give CPU
share and latency guarantees to domains. This is not the default scheduler
and it's got some annoying bug in that's throwing everything off, so it's not
worth enabling for now. Fixing it is on my list of things to do on a slow
weekend ;-)

As Keir says, once you start using services from other domains, things get
rather more complicated regarding latency!

Mark

On Monday 08 Nov 2004 23:50, Andrew W.Donoho wrote:
> Folks,
>
> I know that Xen is designed for servers and such. But defined latency
> (e.g. real time) responsiveness is one of those characteristics that
> needs to be addressed early in the development lifecycle. What are the
> team's thoughts on achieving some sort of latency guarantee. (No fair
> punting by saying that some I/O devices can never guarantee latency,
> those devices do not need to be supported for defined latency
> situations.)
>
> Andrew
>
> ____________________________________
> Andrew W. Donoho
> awd@DDG.com, PGP Key ID: 0x81D0F250
> +1 (512) 453-6652 (o), +1 (512) 750-7596 (m)


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