ARM performance tools apparently missing SPE interrupt in APIC

[Stuart Watt]

I am trying to get the ARM performance assessment setup working (I'm trying to get Mali profiling for OpenCL code) on the Rock 5B+, and I've hit a blocker.

 

The main component to this is some kernel configuration (CONFIG_ARM_SPE_PMU) and a loadable module. Oddly, those work fine in a custom kernel build. What I am hitting appears to be some missing interrupt setup that renders all those components inert. (It has to be a custom build to get CONFIG_ARM_SPE_PMU set.  

 

The issue is that even with the kernel configured and the module loaded, the SPE component remains inactive. ARM has its own system report tool which analyzes a setup, and that tool is reporting an issue:

 

Quote

Actions that can be taken to improve performance tools experience:

  [...]

  Hardware perf events are not available

    ensure APIC table describes PMU interrupt

 

And indeed, nothing seems to show in cat /proc/interrupts. The man page for the module suggests this is the issue: It says:

 

Quote

The SPE interrupt must also be described by the firmware. If the module is loaded and KPTI is disabled (or isn’t required to be disabled) but the SPE PMU still doesn’t show in /sys/bus/event_source/devices/, then it’s possible that the SPE interrupt isn’t described by ACPI or DT. In this case no warning will be printed by the driver.

 

KPTI is definitely disabled and the SPE PMU loads (it's in lsmod) but it still doesn’t show in /sys/bus/event_source/devices/. Nothing relevant seemed to show in dmesg either. 

 

Frankly, I have no idea where to look for the SPE interrupt, or how to set it up. If anybody has any pointers or suggestions, I'd be extremely grateful.