Re: [RFC] CPU controllers?

[Matt Helsley <matthltc@us.ibm.com>]

On Fri, 2006-06-16 at 09:30 +1000, Peter Williams wrote:
> Srivatsa Vaddagiri wrote:

<snip>

> > 	* Supports hard limit and soft limit
> > 	* Introduces new task priorities where tasks that have exceeded their 
> > 	  soft limit can be "parked" until the O(1) scheduler picks them for
> >  	  execution
> > 	* Load balancing on SMP systems made aware of tasks whose execution
> > 	  rate is limited by this feature
> > 	* Patch is simple
> > 
> > Limitations:
> > 	* Does not support guarantee
> 
> Why would a capping mechanism support guarantees?  The two mechanisms 
> can be implemented separately.  The only interaction between them that 
> is required is a statement about which has precedence.  I.e. if a cap is 
> less than a guarantee is it enforced?  I would opine that it should be.

When this combination occurs userspace is crazy/uncoordinated/dumb and
can't be "satisfied". Perhaps the better approach is to ignore both
guarantee and limit (cap) in this case -- treat it as if userspace
hasn't specified either.

Alternatively the kernel can refuse to allow configuring such a
combination in the first place. This is one reason tying guarantees and
limits (caps) into the same framework would be useful.

<snip>

Cheers,
	-Matt Helsley