Re: [PATCH 2/7] xen/events: don't unmask an event channel when an eoi is pending

[Jürgen Groß]

On 08.02.21 11:06, Jan Beulich wrote:
> On 06.02.2021 11:49, Juergen Gross wrote:
> > @@ -1798,6 +1818,29 @@ static void mask_ack_dynirq(struct irq_data *data)
> >   	ack_dynirq(data);
> >   }
> >   
> > +static void lateeoi_ack_dynirq(struct irq_data *data)
> > +{
> > +	struct irq_info *info = info_for_irq(data->irq);
> > +	evtchn_port_t evtchn = info ? info->evtchn : 0;
> > +
> > +	if (VALID_EVTCHN(evtchn)) {
> > +		info->eoi_pending = true;
> > +		mask_evtchn(evtchn);
> > +	}
> > +}
> > +
> > +static void lateeoi_mask_ack_dynirq(struct irq_data *data)
> > +{
> > +	struct irq_info *info = info_for_irq(data->irq);
> > +	evtchn_port_t evtchn = info ? info->evtchn : 0;
> > +
> > +	if (VALID_EVTCHN(evtchn)) {
> > +		info->masked = true;
> > +		info->eoi_pending = true;
> > +		mask_evtchn(evtchn);
> > +	}
> > +}
> > +
> >   static int retrigger_dynirq(struct irq_data *data)
> >   {
> >   	evtchn_port_t evtchn = evtchn_from_irq(data->irq);
> > @@ -2023,8 +2066,8 @@ static struct irq_chip xen_lateeoi_chip __read_mostly = {
> >   	.irq_mask		= disable_dynirq,
> >   	.irq_unmask		= enable_dynirq,
> >   
> > -	.irq_ack		= mask_ack_dynirq,
> > -	.irq_mask_ack		= mask_ack_dynirq,
> > +	.irq_ack		= lateeoi_ack_dynirq,
> > +	.irq_mask_ack		= lateeoi_mask_ack_dynirq,
> >   
> >   	.irq_set_affinity	= set_affinity_irq,
> >   	.irq_retrigger		= retrigger_dynirq,
>
> Unlike the prior handler the two new ones don't call ack_dynirq()
> anymore, and the description doesn't give a hint towards this
> difference. As a consequence, clear_evtchn() also doesn't get
> called anymore - patch 3 adds the calls, but claims an older
> commit to have been at fault. _If_ ack_dynirq() indeed isn't to
> be called here, shouldn't the clear_evtchn() calls get added
> right here?

There was clearly too much time between writing this patch and looking
at its performance impact. :-(

Somehow I managed to overlook that I just introduced the bug here. This
OTOH explains why there are not tons of complaints with the current
implementation. :-)

Will merge patch 3 into this one.


Juergen

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