Re: [Xen-devel] [PATCH v3 32/47] xen/sched: support allocating multiple vcpus into one sched unit

[Jan Beulich <jbeulich@xxxxxxxx>]

On 14.09.2019 10:52, Juergen Gross wrote:
> @@ -366,18 +380,38 @@ static void sched_free_unit(struct sched_unit *unit)
>      xfree(unit);
>  }
>  
> +static void sched_unit_add_vcpu(struct sched_unit *unit, struct vcpu *v)
> +{
> +    v->sched_unit = unit;
> +    if ( !unit->vcpu_list || unit->vcpu_list->vcpu_id > v->vcpu_id )

Is the right side needed? Aren't vCPU-s created in increasing order
of their IDs, and aren't we relying on this elsewhere too?

> +    {
> +        unit->vcpu_list = v;
> +        unit->unit_id = v->vcpu_id;

This makes for a pretty strange set of IDs (non-successive), and
explains why patch 24 uses a local "unit_idx" instead of switching
from v->vcpu_id as array index to unit->unit_id. Is there a reason
you don't divide by the granularity here, eliminating the division
done e.g. ...

> +    }
> +    unit->runstate_cnt[v->runstate.state]++;
> +}
> +
>  static struct sched_unit *sched_alloc_unit(struct vcpu *v)
>  {
>      struct sched_unit *unit, **prev_unit;
>      struct domain *d = v->domain;
>  
> +    for_each_sched_unit ( d, unit )
> +        if ( unit->vcpu_list->vcpu_id / sched_granularity ==

... here. (I also don't see why you don't use unit->unit_id here.)

> @@ -622,9 +659,16 @@ void sched_destroy_vcpu(struct vcpu *v)
>      kill_timer(&v->poll_timer);
>      if ( test_and_clear_bool(v->is_urgent) )
>          atomic_dec(&per_cpu(sched_urgent_count, v->processor));
> -    sched_remove_unit(vcpu_scheduler(v), unit);
> -    sched_free_vdata(vcpu_scheduler(v), unit->priv);
> -    sched_free_unit(unit);
> +    /*
> +     * Vcpus are being destroyed top-down. So being the first vcpu of an unit
> +     * is the same as being the only one.
> +     */
> +    if ( unit->vcpu_list == v )

Interestingly here you rely on there being a certain order.

Jan

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