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xen-devel
Re: [Xen-devel] Re: Fine-grained proxy resource charging
Andi Kleen wrote:
John L Griffin <jlg@xxxxxxxxxx> writes:
> 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.
Consider a xenblk request from different domains that gets merged
into a single request by the elevator. Would you charge the time the
driver spends processing that one to the one domain or the other? Or
a xenblk write the is done in the background by the pdflushd daemons?
There are lots of other cases where IO from different processes gets
"mixed" like this. And in case of Xen you would even need to track IO
from the same process.
Not even standard linux attempts finegrained IO resource tracking and
it would be probably quite complicated and require changes all over
in the host kernel. I don't think it's a particularly good idea.
It's not a bad idea just because it's a hard problem.
As demonstrated in the Usenix paper that John refers to
(http://www.usenix.org/publications/library/proceedings/usenix05/tech/general/cherkasova.html),
the overhead in a driver domain can be very high under certain
circumstances. If you have "customers" sharing domains in a virtual
environment, you have to have some way of charging them fairly for
resource usage. I think the Xen I/O architecture needs to account for
this somehow.
Rob
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