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

[Andi Kleen <ak@xxxxxxx>]

> It's not a bad idea just because it's a hard problem.

Hard, likely slow (x86 has no really cheap
way to do microstate accounting), likely a lot of work,
and you have to fix up every driver in existence for it.
Not even talking about the VM which would need a kind
of redesign for it. For example pdflushd when flushing a dirty page has
no idea who dirtied it originally and there is simply no 
space in struct page to track such stuff.

> 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.

The only sane way would be different driver domains.

-Andi

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