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

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

On Sun, 2015-06-28 at 21:44 -0500, Chong Li wrote:

> +    GC_INIT(ctx);
> +    libxl_scheduler sched = scinfo->sched;
> +    int ret;
> +
> +    if (sched == LIBXL_SCHEDULER_UNKNOWN)
> +        sched = libxl__domain_scheduler(gc, domid);
> +
> +    switch (sched) {
> +    case LIBXL_SCHEDULER_RTDS:
> +        ret = sched_rtds_vcpu_set(gc, domid, scinfo);
> +        break;
> +    default:
> +        LOG(ERROR, "Unknown scheduler");

There are several other known schedulers, I don't think the fact that
they don't have any need for per-vcpu variables should result in this
error message, they should get something more specific to that
situation. Only truly unknown values for the scheduler should result in
this message. 

[...]
>  /*
> + * libxl_vcpu_sched_params is used to get/set per-vcpu params
> +*/
> +#define LIBXL_HAVE_VCPU_SCHED_PARAMS 1
> +
> +/*
> + * libxl_sched_params is used to store per-vcpu params
> +*/
> +#define LIBXL_SCHED_PARAMS 1

Do we need both of these? In particular I'm not sure what the second one
is indicating has changed.

> +
> +/*
>   * libxl ABI compatibility
>   *
>   * The only guarantee which libxl makes regarding ABI compatibility
> @@ -1554,10 +1564,17 @@ int libxl_sched_credit_params_set(libxl_ctx *ctx, uint32_t poolid,
>  #define LIBXL_DOMAIN_SCHED_PARAM_EXTRATIME_DEFAULT -1
>  #define LIBXL_DOMAIN_SCHED_PARAM_BUDGET_DEFAULT    -1
>  
> +/* Per-VCPU parameters*/
> +#define LIBXL_DOMAIN_SCHED_PARAM_VCPU_INDEX_DEFAULT -1

What is the effect of passing vcpuid == -1 to this interface?

Ian.