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

[Meng Xu <xumengpanda@xxxxxxxxx>]

Hi Dario,

On Wed, Sep 13, 2017 at 9:06 PM, Dario Faggioli
<dario.faggioli@xxxxxxxxxx> wrote:
>
> 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)?


I didn't recall that. I should have double checked that I have
resolved every comment in previous patch.
Anyway, I added the comment in the next version, which is comming soon.

>
> 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.


OK. Either works for me. I will go with
return svc->flags & RTDS_extratime.
>
>
> The rest of the patch looks fine to me.


Thanks,

Meng

-- 
Meng Xu
Ph.D. Candidate in Computer and Information Science
University of Pennsylvania
http://www.cis.upenn.edu/~mengxu/

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