Ubuntu
linux package

  1. Bug #1689661
  2. Comment #0

Comment 0 for bug 1689661

Revision history for this message
dann frazier (dannf) wrote :

[Impact]
ACPI-based arm64 systems, such as the Qualcomm QDF2400 and the Hisilicon D05, do not currently have PMU support. This means that tools like perf are unable to use the built-in hardware event counters.

[Test Case]
On an ACPI-based arm64 system, run the following commands:

sudo perf list pmu
sudo perf list hw

Without ACPI PMU support, these will be empty.

[Regression Risk]
The changes are restricted to ARM-specific code, other than an added enum value in linux/cpuhotplug.h. This reduces the non-negligible regression risk to the ARM architecture.

For ACPI-based ARM platforms, regression risk is negligible because they did not have PMU support previously. The non-perf related code is restricted to a change in arch/arm64/kernel/smp.c that saves off pointers to each CPU's MADT GICC tables. The code is populating a static array - so pretty low risk (no pointer dereferences, etc).

The most significant regression risk is to ARM non-ACPI platforms. To mitigate this, we should test this backport on Cavium ThunderX and HP m400 systems.