Re: Cache coherency, clustering, and Kernel virtualization

["Thomas E. Spanjaard" <tgen@xxxxxxxxxxxxx>]

Matthew Dillon wrote:
>     Consider what we want to accomplish.  We want to be able to cut up
>     system resources and link them into 'clusters', with the whole mess
>     tied together on the internet.  Originally I envisioned cutting up
>     memory, disk, and cpu resources and connecting them to a cluster
>     individually, but now I believe what we need to do is connect an
>     entire kernel to the cluster and basically operate as a single system
>     image.

Imho, the ideal situation would be a NUMA SSI cluster.

>     Now consider the problem of tying an entire kernel into an internet-based
>     cluster.  Does that sound like something that would be 'safe' to
>     integrate into your real kernel?  NO WAY!  It is virtually impossible
>     to 'secure' a kernel which is operating as a single system image in
>     a cluster of machines connected together via the internet.

You're right, but clustering 'over the internet' (more popularly, global 
grids) is something that is a typical userspace thing, where you don't 
even need things like NUMA. The tasks you use a global grid for are 
wholly different from a SSI cluster, and I don't think you want to run 
an SSI cluster over the internet with all the latency and insecurity 
involved.

>     What we do is we make it so a DragonFly kernel can be compiled and run
>     as a userland application running under the real DragonFly kernel.  As
>     a userland application the virtual kernel can be completely firewalled
>     off from the rest of the system.  The virtual kernel can then be
>     associated with the 'cluster', and managing controlling memory, cpu,
>     and disk resources is a whole lot easier when you have an entire kernel
>     as your funnel into the real system's resources.  If you want to tie
>     into multiple clusters you just create multiple virtual kernels!  More
>     to the point, the technology could be used to partition off major
>     services and EVEN USER LOGINS(!) on a large machine.

This is hardly the logical step forward beyond SMP, and does nothing to 
make proper use of consumer-level NUMA equipment (AMDs Athlon64/Opteron 
family of processors for example), I don't see multiple virtual kernels 
work in a NUMA system. Or do you intend to not neglect this class of 
machines? :)

Cheers,
--
        Thomas E. Spanjaard
        tgen@xxxxxxxxxxxxx

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