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Re: [Xen-devel] Test result of xen-unstable changeset 25249

On Fri, 2012-04-27 at 09:44 +0100, George Dunlap wrote:
> On 27/04/12 09:21, Dieter Bloms wrote:
> > yes, this is an issue with my patch :( All default values has to be 0, 
> > but only for the credit(2) scheduler cpu_weight must not. So I made a 
> > patch, which set a default of 256 when the cpu_weight isn't set and 
> > credit(2) is used and let it 0 when the scheduler sedf is used. Please 
> > try the attached patch and see if it solve this issue. 
> Dieter,
> Thanks for the patch.  However, I'd really rather avoid putting 
> scheduler defaults in xl if we can at all avoid it.  Defaults should be 
> set in one place, and that should be in the scheduling code itself.
> I think what we really want to do is is any of the parameters are set, 
> after the domain is first created, to read the scheduling parameters for 
> the domain (which will be the defaults), change the ones that are set in 
> the config file, and then write the whole structure back.  That 
> shouldn't be too hard, as libxl__sched_set_params() is called after the 
> domain itself is created;

I guess the low level libxl_sched_*_params_set should take care of this?

>  the main thing is how to tell 
> libxl__sched_set_params() which parameters actually need to be set, and 
> which should be left alone.

Do all of the fields have a spare discriminating value which could mean
"the default". Ideally it would be zero but it doesn't have to be.
Otherwise we can adjust the libxl API to make one available (usually ~0
or similar), the IDL can express these sorts of concepts (see the uses
of init_val).

It may be appropriate to add a libxl__sched_FOO_domain__setdefaults,
which params_set could call to fully initialise the struct (by calling

> Are you up for doing that?  If not, I can put it on my to-do list.
> Thanks,
>   -George

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