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

[Rob Gardner <rob.gardner@xxxxxx>]

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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