Re: [RFC] CPU controllers?

[Nick Piggin]

Sam Vilain wrote:
> Nick Piggin wrote:
>
> > > I think a proportional-share scheduler (which is what a CPU controller
> > > may provide) has non-container uses also. Do you think nice (or sched 
> > > policy) is enough to, say, provide guaranteed CPU usage for 
> > > applications or limit their CPU usage? Moreover it is more flexible 
> > > if guarantee/limit can be specified for a group of tasks, rather than 
> > > individual tasks even in
> > > non-container scenarios (like limiting CPU usage of all web-server 
> > > tasks togther or for limiting CPU usage of make -j command).
> >
> > Oh, I'm sure there are lots of things we *could* do that we currently 
> > can't.
> >
> > What I want to establish first is: what exact functionality is 
> > required, why, and by whom.
>
>
> You make it sound like users should feel sorry for wanting features 
> already commonly available on other high performance unix kernels.

If telling me what exact functionality they want is going to cause them
so much pain, I suppose they should feel sorry for themselves.

And I don't care about any other kernels, unix or not. I care about what
Linux users want.

> The answer is quite simple, people who are consolidating systems and 
> working with fewer, larger systems, want to mark processes, groups of 
> processes or entire containers into CPU scheduling classes, then either 
> fair balance between them, limit them or reserve them a portion of the 
> CPU - depending on the user and what their requirements are. What is 
> unclear about that?

It is unclear whether we should have hard limits, or just nice like
priority levels. Whether virtualisation (+/- containers) could be a
good solution, etc.

If you want to *completely* isolate N groups of users, surely you
have to use virtualisation, unless you are willing to isolate memory
management, pagecache, slab caches, network and disk IO, etc.

> Yes, this does get somewhat simpler if you strap yourself into a 
> complete virtualisation straightjacket, but the current thread is not 
> about that approach - and the continual suggestions that we are all just 
> being stupid and going about it the wrong way are locally off-topic.

I'm sorry you cannot come up with a statement of the functionality you
require without badmouthing "complete" virtualisation or implying that
I'm saying you're stupid.

I think the containers people might also recognise that it may not be
the best solution to make containers the be all and end all of
consolidating systems, and virtualisation is a very relevant topic when
discussing pros and cons and alternate solutions.

But at this point I'm yet to be shown what the *problem* is. I'm not
trying to deny that one might exist.

> Bear in mind that we have on the table at least one group of scheduling 
> solutions (timeslice scaling based ones, such as the VServer one) which 
> is virtually no overhead and could potentially provide the "jumpers" 
> necessary for implementing more complex scheduling policies.

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

--
SUSE Labs, Novell Inc.
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