Commit 61d03862 authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon
Browse files

arm_pmu: fix event CPU filtering 



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

  bd275681 ("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 bd275681 also silently removed the CHAIN event filtering from
armv8pmu_filter(), which will be addressed by a separate patch without
using the filter callback.

Fixes: bd275681 ("perf: Rewrite core context handling")
Reported-by: default avatarJanne Grunau <j@jannau.net>
Link: https://lore.kernel.org/asahi/20230215-arm_pmu_m1_regression-v1-1-f5a266577c8d@jannau.net/


Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Asahi Lina <lina@asahilina.net>
Cc: Eric Curtin <ecurtin@redhat.com>
Tested-by: default avatarJanne Grunau <j@jannau.net>
Link: https://lore.kernel.org/r/20230216141240.3833272-2-mark.rutland@arm.com


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent a428eb4b

arch/arm64/kernel/perf_event.c

+0 −7
Original line number Diff line number Diff line
@@ -1023,12 +1023,6 @@ static int armv8pmu_set_event_filter(struct hw_perf_event *event, 
	return 0;

}



static bool armv8pmu_filter(struct pmu *pmu, int cpu)

{

	struct arm_pmu *armpmu = to_arm_pmu(pmu);

	return !cpumask_test_cpu(smp_processor_id(), &armpmu->supported_cpus);

}



static void armv8pmu_reset(void *info)

{

	struct arm_pmu *cpu_pmu = (struct arm_pmu *)info;
@@ -1258,7 +1252,6 @@ static int armv8_pmu_init(struct arm_pmu *cpu_pmu, char *name, 
	cpu_pmu->stop			= armv8pmu_stop;

	cpu_pmu->reset			= armv8pmu_reset;

	cpu_pmu->set_event_filter	= armv8pmu_set_event_filter;

	cpu_pmu->filter			= armv8pmu_filter;



	cpu_pmu->pmu.event_idx		= armv8pmu_user_event_idx;

drivers/perf/arm_pmu.c

+1 −7
Original line number Diff line number Diff line
@@ -550,13 +550,7 @@ static void armpmu_disable(struct pmu *pmu) 
static bool armpmu_filter(struct pmu *pmu, int cpu)

{

	struct arm_pmu *armpmu = to_arm_pmu(pmu);

	bool ret;



	ret = cpumask_test_cpu(cpu, &armpmu->supported_cpus);

	if (ret && armpmu->filter)

		return armpmu->filter(pmu, cpu);



	return ret;

	return !cpumask_test_cpu(cpu, &armpmu->supported_cpus);

}



static ssize_t cpus_show(struct device *dev,

include/linux/perf/arm_pmu.h

+0 −1
Original line number Diff line number Diff line
@@ -100,7 +100,6 @@ struct arm_pmu { 
	void		(*stop)(struct arm_pmu *);

	void		(*reset)(void *);

	int		(*map_event)(struct perf_event *event);

	bool		(*filter)(struct pmu *pmu, int cpu);

	int		num_events;

	bool		secure_access; /* 32-bit ARM only */

#define ARMV8_PMUV3_MAX_COMMON_EVENTS		0x40