Re: [PATCH v7 for Xen 4.7 3/4] libxl: enable per-VCPU parameter settings for RTDS scheduler

[Dario Faggioli <dario.faggioli@citrix.com>]

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On Wed, 2016-03-16 at 11:47 -0500, Chong Li wrote:
> Add libxl_vcpu_sched_params_get/set and sched_rtds_vcpu_get/set
> functions to support per-VCPU settings.
> 
And a couple more things that I forgot.

I'd shorten the subject line, as already suggested for libxc.

> +/* Get the RTDS scheduling parameters of vcpu(s) */
> +static int sched_rtds_vcpu_get(libxl__gc *gc, uint32_t domid,
> +                               libxl_vcpu_sched_params *scinfo)
> +{
I think this should be called

static int sched_rtds_vcpu_params_get(libxl__gc *gc, uint32_t domid,
                                      libxl_vcpu_sched_params *scinfo)

for homogeneity with the _set counterpart here below:

> @@ -5873,6 +6048,74 @@ int libxl_domain_sched_params_set(libxl_ctx
> *ctx, uint32_t domid,
>      return ret;
>  }
>  
> +int libxl_vcpu_sched_params_set(libxl_ctx *ctx, uint32_t domid,
> +                                const libxl_vcpu_sched_params
> *scinfo)
> +{
So, this function takes a libxl_vcpu_sched_params*, which is basically
an array of vcpus' parameters, one element per vcpu (and it can be
sparse).

Are there any restrictions on how such array should be constructed, for
calling this function? Are they any special meaning of particular
configurations of the array?

I think at least the latter is true, in fact:
 - this calls sched_rtds_vcpus_params_set();
 - in there, if the array is empty, we fail;
 - if the array has one or more elements, we deal with the vcpus 
   (and just them) specified in the elements of the array itself.

Then there is libxl_vcpu_sched_params_set_all(). That one:
 - calls sched_rtds_vcpus_params_set_all();
 - in there, if the array has more than just one element, we fail.

And then the get side, with libxl_vcpu_sched_params_get(). That one:
 - calls sched_rtds_vcpu_get();
 - in there, if the array is empty, we create one, and return info for 
   all the vcpus;
 - if the array has one or more elements, we deal with them (and just 
   them).

I think this should be documented some (unless it's already there and I
missed it).

Thanks and Regards again,
Dario
-- 
<<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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