I am looking into how to charge a domain (say, domain "A") for the
resources consumed by other service domains (say, B) on behalf of A. For
example, charging A for the CPU cycles consumed by the network I/O domain
(B) as it processes packets produced or consumed by A.
The HP folks recently demonstrate a useful first step (see the Usenix 2005
paper and the xen-devel post "Yet another Xen performance monitoring tool"
on 2005-08-18): count the number of page swaps between A and B (as well as
C and B, D and B, etc.) and use that to approximate how much of B's CPU
usage should be assigned to A (and C, D, etc.)
I'm pursuing more cycle-accurate methods, in anticipation of non-dom0
service domains that will do variable amounts of proxy processing,
especially where the resources consumed (CPU, memory, I/O, larger
primitives) are not correlated with the amount of interdomain traffic
between A and B. For example, a lightweight version of Resource
Containers (Banga, OSDI 1999) or similar concepts.
The eventual goal would be for B itself to calculate and specify to Xen
the amount of processing it does on behalf of A and other domains. Looking
ahead, a possible next step is for Xen to expose to B whether or not A has
already exceeded its periodic resource allocation, so any schedulers
inside B can make smarter decisions: for example, not processing packets
for A when A has temporarily exhausted its allocation.
There aren't many technical details yet; my objective here is to
synchronize with anyone who's also been thinking about this particular
problem.
-John
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