Mark Rutland 61d0386273 arm_pmu: fix event CPU filtering ...

Janne reports that perf has been broken on Apple M1 as of commit:

  bd27568117 ("perf: Rewrite core context handling")

That commit replaced the pmu::filter_match() callback with
pmu::filter(), whose return value has the opposite polarity, with true
implying events should be ignored rather than scheduled. While an
attempt was made to update the logic in armv8pmu_filter() and
armpmu_filter() accordingly, the return value remains inverted in a
couple of cases:

* If the arm_pmu does not have an arm_pmu::filter() callback,
  armpmu_filter() will always return whether the CPU is supported rather
  than whether the CPU is not supported.

  As a result, the perf core will not schedule events on supported CPUs,
  resulting in a loss of events. Additionally, the perf core will
  attempt to schedule events on unsupported CPUs, but this will be
  rejected by armpmu_add(), which may result in a loss of events from
  other PMUs on those unsupported CPUs.

* If the arm_pmu does have an arm_pmu::filter() callback, and
  armpmu_filter() is called on a CPU which is not supported by the
  arm_pmu, armpmu_filter() will return false rather than true.

  As a result, the perf core will attempt to schedule events on
  unsupported CPUs, but this will be rejected by armpmu_add(), which may
  result in a loss of events from other PMUs on those unsupported CPUs.

This means a loss of events can be seen with any arm_pmu driver, but
with the ARMv8 PMUv3 driver (which is the only arm_pmu driver with an
arm_pmu::filter() callback) the event loss will be more limited and may
go unnoticed, which is how this issue evaded testing so far.

Fix the CPU filtering by performing this consistently in
armpmu_filter(), and remove the redundant arm_pmu::filter() callback and
armv8pmu_filter() implementation.

Commit bd27568117 also silently removed the CHAIN event filtering from
armv8pmu_filter(), which will be addressed by a separate patch without
using the filter callback.

Fixes: bd27568117 ("perf: Rewrite core context handling")
Reported-by: Janne Grunau <[email protected]>
Link: https://lore.kernel.org/asahi/[email protected]/
Signed-off-by: Mark Rutland <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ravi Bangoria <[email protected]>
Cc: Asahi Lina <[email protected]>
Cc: Eric Curtin <[email protected]>
Tested-by: Janne Grunau <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

2023-02-16 21:23:52 +00:00

..

arm_pmu.h

arm_pmu: fix event CPU filtering

2023-02-16 21:23:52 +00:00

riscv_pmu.h

perf: RISC-V: exclude invalid pmu counters from SBI calls

2022-09-08 13:34:50 -07:00