Re: Re: Losing PS/2 Interrupts

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Fri, May 20, 2011 at 11:53:54AM -0400, Thomas Goetz wrote:
> 
> On May 19, 2011, at 5:45 PM, Thomas Goetz wrote:
> 
> > I'm running PVOPs 2.6.38 on Xen 4.0.2 RC3 and while booting a guest I lose interrupts for the PS/2 trackpad. The trackpad stops functioning because the device is waiting for service. I added a work around that calls i8042_interupt form a timer if it hasn't been called in 1s and it started working again. I added some code to Xen to count IRQ 12 and compared that to the IRQ 12 count in //proc/interrupts (I stopped PS/2 activity and waited for PS/2 interrupt activity to stop before taking the counts). I lose one interrupt in Dom0 every time the trackpad freezes.
> > 
> > 
> > (XEN) IRQ 12 count 21048
> > 12:      21047          0  xen-pirq-ioapic-edge  i8042   <--- lost an interrupt in dom0
> > ...
> > 
> > (XEN) IRQ 12 count 48540
> > 12:      48537          0  xen-pirq-ioapic-edge  i8042   <--- lost 3 interrupts in dom0
> > 
> > 
> > I looked at the point at which the trackpad gets it's last interrupt in a trace and the other major activity at that time is the event channel that services the Qemu vcpu io_req code.
> > 
> > This 2.6.38 tree has a merge of Stafano's 2.6.39 fixes in drivers/xen/events.c.
> > 
> > Anyone have any ideas or suggestions?
> > 
> 
> 
> More data. The number of missing interrupts is equal to the number of times __do_IRQ_guest called send_guest_pirq and incremented already_pending. The number of IRQ 12 interrupts reported by /proc/interrupts is the same as the count of times __xen_evtchn_do_upcall called generic_handle_irq_desc for IRQ 12. So the issue has to be between send_guest_pirq in Xen and  __xen_evtchn_do_upcall in dom0.

So extremly hairy code. Not sure if there was any work done in the send_guest_pirq, but I do
know that __xen_evtchn_do_upcall had a fair bit of IRQ fair round-robin code added in.

The git commits were

3b7bcdf xen: events: Remove redundant clear of l2i at end of round-robin loop
24b51c2 xen: events: Make round-robin scan fairer by snapshotting each l2 word once only
ada6814 xen: events: Clean up round-robin evtchn scan.
f1f4a32 xen: events: Make last processed event channel a per-cpu variable.
ab7f863 xen: events: Process event channels notifications in round-robin order.