[Xen-devel] Question about the general performance counter overflow interrupt handling

[Meng Xu <mengxu@xxxxxxxxxxxxxx>]

Hi Jan and Boris,

I'm Meng Xu from the University of Pennsylvania.

I'm wondering:
How does Xen (vpmu) handle the general performance counter's overflow interrupt?
Could you point me to the function handler, if Xen does handle it?

---What I want to achieve---
I'm looking at the real-time performance in Xen.
I want to profile the system's status for every K L3 cache misses from
a specific core.
I plan to program the general performance counter to -K to trigger an
overflow interrupt. In the interrupt handler, I plan to check the
system's status and give hints to the scheduler.

--- What I have tried ---
I want to find the interrupt handler and plug in another function.
1) I checked Xen's vpmu command option, it does not say vpmu handles
the general performance counter's overflow interrupt.

2) I also added a function inside pmu_apic_interrupt() in apic.c.
However, it seems that the pmu_apic_interrupt() is not triggered when
the general performance counter overflows.

When I program the general performance counter to trigger an overflow
interrupt, I set the following bits for the event selector register
and run a task to generate the L3 cache cache miss.
FLAG_ENABLE: 0x400000UL
FLAG_INT:    0x100000UL
FLAG_USR: 0x010000UL
L3_ALLMISS_EVENT    0x2E
L3_ALLMISS_MESI     0x41

I'm sure the performance counter does overflow, but I didn't see any
interrupt was triggered. Maybe I missed something?

Thank you very much for your help and time!

Best regards,

Meng
-----------
Meng Xu
PhD Candidate in Computer and Information Science
University of Pennsylvania
http://www.cis.upenn.edu/~mengxu/

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