Re: [Xen-devel] [PATCH 01/19] xen: sched: leave CPUs doing tasklet work alone.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.06.16 at 01:11, <dario.faggioli@xxxxxxxxxx> wrote:
> --- a/xen/common/sched_credit.c
> +++ b/xen/common/sched_credit.c
> @@ -1819,24 +1819,24 @@ csched_schedule(
>      else
>          snext = csched_load_balance(prv, cpu, snext, &ret.migrated);
>  
> + out:
>      /*
>       * Update idlers mask if necessary. When we're idling, other CPUs
>       * will tickle us when they get extra work.
>       */
> -    if ( snext->pri == CSCHED_PRI_IDLE )
> +    if ( tasklet_work_scheduled || snext->pri != CSCHED_PRI_IDLE )
>      {
> -        if ( !cpumask_test_cpu(cpu, prv->idlers) )
> -            cpumask_set_cpu(cpu, prv->idlers);
> +        if ( cpumask_test_cpu(cpu, prv->idlers) )
> +            cpumask_clear_cpu(cpu, prv->idlers);
>      }
> -    else if ( cpumask_test_cpu(cpu, prv->idlers) )
> +    else if ( !cpumask_test_cpu(cpu, prv->idlers) )
>      {
> -        cpumask_clear_cpu(cpu, prv->idlers);
> +        cpumask_set_cpu(cpu, prv->idlers);
>      }

Is there a reason for this extra code churn? It would seem to me
that the change could be just the "out" label movement and
adjustment to the first if:

   if ( !tasklet_work_scheduled && snext->pri == CSCHED_PRI_IDLE )

Am I overlooking something?

Jan


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