Re: [RFC v2 PATCH 0/8] CFS Hard limits - v2

[Srivatsa Vaddagiri <vatsa@in.ibm.com>]

On Wed, Sep 30, 2009 at 07:55:37PM +0530, Bharata B Rao wrote:
> On Wed, Sep 30, 2009 at 05:36:29PM +0400, Pavel Emelyanov wrote:
> > Bharata B Rao wrote:
> > > Hi,
> > > 
> > > Here is the v2 post of hard limits feature for CFS group scheduler. This
> > > RFC post mainly adds runtime borrowing feature and has a new locking scheme
> > > to protect CFS runtime related fields.
> > > 
> > > It would be nice to have some comments on this set!
> > 
> > I have a question I'd like to ask before diving into the code.
> > Consider I'm a user, that has a 4CPUs box 2GHz each and I'd like
> > to create a container with 2CPUs 1GHz each. Can I achieve this
> > after your patches?
> 
> I am not sure if I understand the GHz specification you mention here.
> Are you saying that you want run a container with 2 CPUS with each of
> them running at half their (frequency)capacity ?
> 
> This hard limits scheme is about time based rate limiting where you can
> specify a runtime(=hard limit) and a period for the container and the
> container will not be allowed to consume more than the specified CPU time
> within a given period.

IMO Pavel's requirement can be met with a hard limit of 25%

	2 CPU of 1GHz = (1/2 x 4) (1/2 x 2) GHz CPUs
		      = 1/4 x 4 2GHz CPU
		      = 25% of (4 2GHz CPU)

IOW by hard-limiting a container thread to run just 0.5sec every sec on a 2GHz 
cpu, it is effectively making progress at the rate of 1GHz?

- vatsa