Re: [Xen-devel] [PATCH] xen: idle_loop: either deal with tasklets or go idle

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Fri, 2017-06-16 at 10:41 -0700, Stefano Stabellini wrote:
> On Fri, 16 Jun 2017, Dario Faggioli wrote:
> > 
> > diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
> > index 76310ed..86cd612 100644
> > --- a/xen/arch/arm/domain.c
> > +++ b/xen/arch/arm/domain.c
> > @@ -41,20 +41,28 @@ DEFINE_PER_CPU(struct vcpu *, curr_vcpu);
> >  
> >  void idle_loop(void)
> >  {
> > +    unsigned int cpu = smp_processor_id();
> > +
> >      for ( ; ; )
> >      {
> > -        if ( cpu_is_offline(smp_processor_id()) )
> > +        if ( cpu_is_offline(cpu) )
> >              stop_cpu();
> >  
> > -        local_irq_disable();
> > -        if ( cpu_is_haltable(smp_processor_id()) )
> > +        /* Are we here for running vcpu context tasklets, or for
> > idling? */
> > +        if ( cpu_is_haltable(cpu) )
> >          {
> > -            dsb(sy);
> > -            wfi();
> > +            local_irq_disable();
> > +            /* We need to check again, with IRQ disabled */
> > +            if ( cpu_is_haltable(cpu) )
> > +            {
> > +                dsb(sy);
> > +                wfi();
> > +            }
> > +            local_irq_enable();
> >          }
> > -        local_irq_enable();
> > +        else
> > +            do_tasklet();
> >  
> > -        do_tasklet();
> >          do_softirq();
> 
> Are you sure you want to check that cpu_is_haltable twice? It doesn't
> make sense to me.
>
It's because of IRQ being disabled the first time.

But anyway, discard this patch. I'll go back to (a slightly modified
version of) the first one I sent, which defines a tasklet specific
helper function.

I'll send it on Monday.

Regards,
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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