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Re: [Xen-devel] [PATCH v3 for Xen 4.6 3/4] libxl: enable per-VCPU parameter settings for RTDS scheduler

On Wed, 2015-07-08 at 09:35 -0500, Chong Li wrote:
> On Tue, Jul 7, 2015 at 11:23 AM, Dario Faggioli

> >>
> >> +/* Per-VCPU parameters*/
> >> +
> >>  int libxl_domain_sched_params_get(libxl_ctx *ctx, uint32_t domid,
> >>                                    libxl_domain_sched_params *params);
> >>  int libxl_domain_sched_params_set(libxl_ctx *ctx, uint32_t domid,
> >>                                    const libxl_domain_sched_params 
> >> *params);
> >> +int libxl_vcpu_sched_params_get(libxl_ctx *ctx, uint32_t domid,
> >> +                                  libxl_vcpu_sched_params *params);
> >> +int libxl_vcpu_sched_params_set(libxl_ctx *ctx, uint32_t domid,
> >> +                                  const libxl_vcpu_sched_params *params);
> >>
> > Didn't we say that we wanted the fact that now, at least for RTDS,
> > libxl_domain_sched_params_*() deals with default parameters to be
> > documented in a comment somewhere? Have I missed it?
> I'll implement it in the next version.
> Do both get/set deal with default parameters? I can easily implement
> it in hypervisor, because default parameters
> (RTDS_DEFAULT_PERIOD/BUDGET) are just defined there. But for libxl,
> how do I deal with it without knowing the default values?
What I meant was that I am ok with this being implemented in the
hypervisor, but I think we want a comment explaining the difference
between the two sets of operations (the _domain_ one and the _vcpu_ one)
here in the library too.

And in such a comment, it would be good to mention what the _domain_
call does for a scheduler that supports per-vcpu parameters (and the
vice-versa, which, yes, is rather trivial, but still).

The aim would be to give an libxl user an idea of what function he/she
wants, depending on what scheduler and on which parameter, to achieve
its purposes, and what (kind of error/behavior) should be expected if
the wrong one is used.

<<This happens because I choose it to happen!>> (Raistlin Majere)
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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