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Re: [Xen-devel] Re: Fine-grained proxy resource charging

To: Andi Kleen <ak@xxxxxxx>
Subject: Re: [Xen-devel] Re: Fine-grained proxy resource charging
From: Rob Gardner <rob.gardner@xxxxxx>
Date: Mon, 22 Aug 2005 09:08:51 -0600
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, John L Griffin <jlg@xxxxxxxxxx>
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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.


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