** Changed in: linux (Ubuntu Zesty)
Status: In Progress => Fix Committed
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https://bugs.launchpad.net/bugs/1689661
Title:
No PMU support for ACPI-based arm64 systems
Status in linux package in Ubuntu:
Fix Committed
Status in linux source package in Zesty:
Fix Committed
Bug description:
[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 limited because they
did not have PMU support previously. However, if this code is buggy,
previously working commands that just made use of non-PMU events (e.g.
perf top) might start causing problems. To mitigate this, I did a
perf_fuzzer run on a QDF2400 (ACPI-based) and confirmed it survived
(Note: this included a workaround for LP: #1689855, which will need to
be fixed separately once upstreamed).
For non-ACPI-based (i.e. devicetree) ARM platforms, there is a chance
that the changes have broken PMU support. To mitigate that, I also did
a perf_fuzzer run on a Cavium ThunderX system booted in DT mode, which
it survived.
Finally, the non-perf related changes in this series are 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 with
existing data - so pretty low risk (no pointer dereferences, etc).
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