Re: [Xen-devel] [PATCH] full support of setting scheduler parameters on domain creation

[Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>]

On 05/21/2012 03:53 PM, Ian Campbell wrote:
> On Mon, 2012-05-21 at 14:48 +0100, George Dunlap wrote:
> > On Mon, May 21, 2012 at 2:34 PM, Ian Campbell<Ian.Campbell@xxxxxxxxxx>  wrote:
> > > > Hmm. Scheduling parameters are handled in the hypervisor. I don't want to
> > > > export the knowledge about semantics to the tools. If this is no problem,
> > > > why can't I just set the defaults in the tools and omit asking the
> > > > hypervisor for the current settings?
> > > Exporting the idea that 0 is not a valid weight is (IMHO at least)
> > > better than exporting the fact that the default weight is (e.g.) 200 and
> > > hard coding that in multiple places.
> > I agree.
> >
> > > You could define a symbolic name if that would make you more comfortable
> > > (that would allow us to change the specific value without changing the
> > > API)
> > That is, as long as the "reasonable value" is the same for all of the
> > parameters.
> I actually meant a symbolic name for the default of each, rather than
> one for all of them.
-1 would fit for all parameters. This value is either invalid or "don't care".

> > I half wonder if having an "init schedule params" function which would
> > set each value to the default for that value would be useful, or if it
> > would be overkill.
> >
> > Of course, if we're doing that, it's only one step further to just
> > reading the actual scheduler parameters...
> I suppose we could make the autogenerated libxl_sched_params_init
> instead be a hand-coded thing which actually reads them.
Reading the scheduler parameters would require a new hypervisor interface
(e.g. a new sub-command of XEN_DOMCTL_scheduler_op) which will have to be
implemented by all schedulers supporting parameter changes.

I think this would be the cleanest solution. If this is the way to go, I
can prepare a patch.

BTW: I just discovered the first patch was not complete, as the original
coding to select the scheduler didn't take cpupools into account. It just
selected the default scheduler instead of the cpupool specific one.


Juergen

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Juergen Gross                 Principal Developer Operating Systems
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