Re: [Xen-devel] [PATCH 07/60] xen/sched: build a linked list of struct sched_unit

[Juergen Gross <jgross@xxxxxxxx>]

On 19.07.19 02:01, Dario Faggioli wrote:
> On Tue, 2019-05-28 at 12:32 +0200, Juergen Gross wrote:
> > In order to make it easy to iterate over sched_unit elements of a
> > domain build a single linked list and add an iterator for it.
> How about a ',' between domain and build?
Okay.

> > For completeness add another iterator for_each_sched_unit_vcpu()
> > which
> > will iterate over all vcpus if a sched_unit (right now only one).
> > This
> "over all vcpus of a sched_unit" ?
Oh, of course!

> > will be needed later for larger scheduling granularity (e.g. cores).
> >
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> One question:
>
> > @@ -279,8 +279,16 @@ struct vcpu
> >   struct sched_unit {
> >       struct vcpu           *vcpu;
> >       void                  *priv;      /* scheduler private data */
> > +    struct sched_unit     *next_in_list;
> >   };
> >   
> > +#define for_each_sched_unit(d,
> > e)                                         \
> > +    for ( (e) = (d)->sched_unit_list; (e) != NULL; (e) = (e)-
> > > next_in_list )
> > +
> > +#define for_each_sched_unit_vcpu(i,
> > v)                                    \
> > +    for ( (v) = (i)->vcpu; (v) != NULL && (v)->sched_unit ==
> > (i);         \
> > +          (v) = (v)->next_in_list )
> > +
> So, here... sorry if it's me not seeing it, but why the
> (v)->sched_unit == (i) check is necessary?
>
> Do we expect to put in the list of vcpus of a particular unit, vcpus
> that are in another unit?
Yes. I'm making use of the fact that all vcpus in a unit are consecutive
as I'm re-using the already existing list of vcpus in a domain:

dom->vcpu0->vcpu1->vcpu2->vcpu3
      ^             ^
      !             !
unit0-+             !
                    !
unit2---------------+


Juergen

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