Re: [RFC] CPU controllers?

From: Nick Piggin
Date: Sun Jun 18 2006 - 03:27:34 EST


Andrew Morton wrote:
On Sun, 18 Jun 2006 16:11:18 +1000
Nick Piggin <nickpiggin@xxxxxxxxxxxx> wrote:


If you want to *completely* isolate N groups of users, surely you
have to use virtualisation,


I'd view this as a kludge. If one group of tasks is trashing the
performance of another group of tasks the user is forced to use hardware
virtualisation to work around it.

I mean, is this our answer to the updatedb problem? Instantiate a separate
copy of the kernel just to run updatedb?

Well even before that, I'd view the fact that working around the VM's
poor behaviour by putting updatedb into a container or memory control
as a kludge anyway. CPU and IO control (ie. nice & ioprio) is reasonable.

updatedb is pretty simple and the VM should easily be able to recognise
its use-once nature.

However I don't doubt that people would like to be able to manage memory
better. Whether that is best served by having resource control heirarchies
or virtualisation or something else completely is still on the table IMO.



unless you are willing to isolate memory
management, pagecache, slab caches, network and disk IO, etc.


Well yes. Ideally and ultimately. People have done this, and it's in
production. We need to see (and work upon) the patches before we can judge
whether we want to do this, and how far we want to go.

Definitely.



Again, I don't care about the solutions at this stage. I want to know
what the problem is. Please?


Isolation. To prevent one group of processes from damaging the performance
of other groups, by providing manageability of the resource consumption of
each group. There are plenty of applications of this, not just
server-consolidation-via-server-virtualisation.

OK... let me put it more clearly. What are the requirements?
I don't like that apparently virtualisation can't be discussed in
a general thread about resource control. Nothing is going to be a
100% solution for everybody. If, for a *specific* application,
virtualisation can be discounted... then great, that is the kind
of discussion I would like to see.

--
SUSE Labs, Novell Inc.
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