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



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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