Re: [RFC] [Design] Better XL support of RTDS scheduler for Xen 4.6

[Ian Campbell <ian.campbell@citrix.com>]

On Mon, 2015-02-23 at 22:58 -0500, Meng Xu wrote:
> I'm not sure if other schedulers need such functionality right now,
> because the credit2 scheduler account for the credit based on each
> domain instead of each VCPU. But if the scheduler will consider the
> vcpu-level credit/budget accounting, this could be helpful.

We should take it as given that some other scheduler will want
vcpu-level parameters in the future and decide now how we want that
interface to look across multiple schedulers now, with the big question
I suppose being a large union struct vs individual structs (and perhaps
a KeyedUnion).

At the domain level param level we have libxl_domain_sched_params in
libxl_domain_build_info and via libxl_domain_sched_params_set/get.

We also have libxl_sched_credit_params and
libxl_sched_credit_params_get/set for the credit scheduler, but not for
other scheduler types.

I don't recall how we ended up with both, are the credit ones
deprecated/legacy and the combined one the One True Way or the other way
around?

In any case, we should decide what we want for both per-domain and
per-vcpu parameters, with one eye on the libxl API guarantees, and try
and have them at least be somewhat consistent.

Ian.