Re: [PATCH v2 1/5] xen:rtds: towards work conserving RTDS

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

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On Fri, 2017-09-01 at 11:58 -0400, Meng Xu wrote:
> Make RTDS scheduler work conserving without breaking the real-time
> guarantees.
> 
> VCPU model:
> Each real-time VCPU is extended to have an extratime flag
> and a priority_level field.
> When a VCPU's budget is depleted in the current period,
> if it has extratime flag set,
> its priority_level will increase by 1 and its budget will be
> refilled;
> othewrise, the VCPU will be moved to the depletedq.
> 
> Scheduling policy is modified global EDF:
> A VCPU v1 has higher priority than another VCPU v2 if
> (i) v1 has smaller priority_leve; or
> (ii) v1 has the same priority_level but has a smaller deadline
> 
> Queue management:
> Run queue holds VCPUs with extratime flag set and VCPUs with
> remaining budget. Run queue is sorted in increasing order of VCPUs
> priorities.
> Depleted queue holds VCPUs which have extratime flag cleared and
> depleted budget.
> Replenished queue is not modified.
> 
Mmm.. didn't we agree about putting a word of explanation of how the
spare bandwidth ends up being distributed (i.e., in a way which is
proportional to the utilization)? Or is it there and it's me that am
not finding it?

> --- a/xen/common/sched_rt.c
> +++ b/xen/common/sched_rt.c 
> @@ -245,6 +258,11 @@ static inline struct list_head *rt_replq(const
> struct scheduler *ops)
>      return &rt_priv(ops)->replq;
>  }
>  
> +static inline bool has_extratime(const struct rt_vcpu *svc)
> +{
> +    return (svc->flags & RTDS_extratime) ? 1 : 0;
> +}
> +
'true' and 'false'. But I think

 return svc->flags & RTDS_extratime

is just fine already, without any need for the ?: operator.

The rest of the patch looks fine to me.

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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