Re: [Xen-devel] xen and virtual iron

[Andrew Theurer <habanero@xxxxxxxxxx>]

Sean Harper wrote:

> At Linuxworld a company called Virtual Iron is demoing a product that,
> like Xen or VMWare, can break physical machines into virtual machines.
>
> However, unlike Xen or VMWare, this product can also aggregate physical
> machines into virtual machines.  In other words, it is possible for the
> user to specify that 3.5 cpus from 2 machines (2 from 1 and 1.5 from
> another) be assigned to a virtual machine. When linux boots on that
> virtual machine it simply looks like a 4 cpu machine (but 1 of the cpus
> is slower). Presumably there is a pretty big performance penalty for
> sharing across machines, which they mitigate to some extent by requiring
> Infiniband.
>
> It seems like most of the tricky work is around caching to optimize the
> performance across the slower communication bus (when sharing between
> machines).
>  
Hmm, sounds like a NUMA system, with a relatively low throughput and 
high latency interconnect.   Not sure if anyone would want to do this on 
a workload where performance matters.
I suppose with a layer of abstraction like Xen, doing something like 
this is feasible.  You could leverage the NUMA code in the linux kernel, 
but I would think you would need a very highly parallel workload to make 
this effective, and if you have that, a cluster setup would probably 
work just as well anyway.
-Andrew Theurer


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