Re: [PATCH 06/16] sched: SCHED_DEADLINE push and pull logic

[Juri Lelli]

On 04/07/2012 04:32 AM, Hillf Danton wrote:
> On Sat, Apr 7, 2012 at 1:31 AM, Juri Lelli<juri.lelli@xxxxxxxxx>  wrote:
> > > >   kernel/sched_dl.c |  912
> > > >   kernel/sched_rt.c |    2 +-
>
> You are working on 2.6.3x, x<= 8 ?
> If so, what is the reason(just curious)?
> Already planned to add in 3.3 and above?

Dario answered on this :-).
  
> > > > +               if (!dl_entity_preempt(&entry->dl,&p->dl))
> > >
> > >                 if (dl_entity_preempt(&p->dl,&entry->dl))
> >
> > Any specific reason to reverse the condition?
> Just for easing readers.

Ok, reasonable. Here and below.

> > > > +select_task_rq_dl(struct task_struct *p, int sd_flag, int flags)
> > > > +{
> > > > +       struct task_struct *curr;
> > > > +       struct rq *rq;
> > > > +       int cpu;
> > > > +
> > > > +       if (sd_flag != SD_BALANCE_WAKE)
> > >
> > >                 why is task_cpu(p) not eligible?
> >
> > Right, I'll change this.
> No, you will first IMO sort out clear answer to the question.

task_cpu(p) is eligible and will be returned if sd_flag != SD_BALANCE_WAKE
&& sd_flag != SD_BALANCE_FORK as in sched_rt. I changed the code accordingly.

> > > > +           (rq->curr->dl.nr_cpus_allowed<    2 ||
> > > > +            dl_entity_preempt(&rq->curr->dl,&p->dl))&&
> > >
> > >                 !dl_entity_preempt(&p->dl,&rq->curr->dl))&&
> >
> > As above?
> Just for easing reader.
>
> > > > +#ifdef CONFIG_SMP
> > > > +       /*
> > > > +        * In the unlikely case current and p have the same deadline
> > > > +        * let us try to decide what's the best thing to do...
> > > > +        */
> > > > +       if ((s64)(p->dl.deadline - rq->curr->dl.deadline) == 0&&
> > > > +           !need_resched())
> > >
> > > please recheck !need_resched(), say rq->curr need reschedule?
> >
> > Sorry, I don't get this..
> Perhaps smp_processor_id() != rq->cpu

need_resched is actually checked...

> > >         if (task_running(rq, p))
> > >                 return 0;
> > >         return cpumask_test_cpu(cpu,&p->cpus_allowed);
> >
> > We use this inside pull_dl_task. Since we are searching for a task to
> > pull, you must be sure that the found task can actually migrate checking
> > nr_cpus_allowed>  1.
> If cpu is certainly allowed for task to run, but nr_cpus_allowed is no more
> than one, which is corrupted?
>
> > Well, ok with this and above. Anyway this code is completely removed in
> > 15/16.
> Yup, another reason for monolith.

Monolithic is below. Anyway, please check the github repo for bug
fixes/new features. ;-)

> > > > +
> > > > +static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);
> > > > +
> > > > +static int find_later_rq(struct task_struct *task)
> > > > +{
> > > > +       struct sched_domain *sd;
> > > > +       struct cpumask *later_mask = __get_cpu_var(local_cpu_mask_dl);
> > >
> > >         please check is local_cpu_mask_dl valid
> >
> > Could you explain more why should I check for validity?
> Only for the case that something comes in before it is initialized,
> IIRC encountered by Steven.

Do you mean at kernel_init time?
Could you be more precise about the problem Steven encountered?

> > Ok, I'll prepare the monolithic patch and probably store it somewhere so
> > that it can be downloaded also by others.
> Info Hillf once it is ready, thanks.

Here we go:
https://github.com/downloads/jlelli/sched-deadline/sched-dl-V4.patch

I noticed that the Cc list is changed... something went wrong?
Anyway, I restored it to the original one. :-)

Thanks and Regards,

- Juri
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