Rik van Riel and Chris Wright discussed virtualization. This is currently
a hot topic, and several OLS sessions will be dedicated to it in the next
few days. At the kernel level, however, it seems that there are not a
whole lot of issues which need to be resolved.
Virtual hosts may have multiple virtual processors; they will schedule
processes between them. The physical host may also have multiple
processors, and it will be performing its own scheduling. Since the two
levels know little about each other, scheduling imbalances can result. Xen
does a certain amount of "rotating" processes around to deal with this
problem. Despite being discussed for a while, this issue does not appear
to be particularly serious.
It was pointed out that the various virtualization implementations (Xen and
user-mode Linux in particular) have their own virtual buses, virtual
drivers, etc. Might there be some benefit in merging them? Perhaps, but
the amount of code involved is quite small.
Merging Xen. The Xen patches create a completely new architecture for the
virtual machine. There have been objections to this approach; it looked
like a maintenance problem, especially as Xen is ported to more real
architectures. So the patches are being reworked, and the
arch/xen directory is going away. Stuff which is truly specific
to Xen will find its way into the drivers or host architecture
directories. With these changes made, opposition to the merging of Xen
should be much reduced.
Linus had to ask: is anybody actually using Xen? The biggest users are, as
expected, in the virtual hosting business. Most of them are still in
relatively early evaluation stages - Xen is a young technology. Xen is
also heavily used by people who want to play with multiple distributions or
otherwise need sandbox systems to work with.
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