[PATCH V7 3/6] arm64/perf: Add branch stack support in struct arm_pmu

Anshuman Khandual
2023-01-05T18:52:05Z

This updates 'struct arm_pmu' for branch stack sampling support later. This
adds a new 'features' element in the structure to track supported features,
and another 'private' element to encapsulate implementation attributes on a
given 'struct arm_pmu'. These updates here will help in tracking any branch
stack sampling support, which is being added later. This also adds a helper
arm_pmu_branch_stack_supported().

This also enables perf branch stack sampling event on all 'struct arm pmu',
supporting the feature but after removing the current gate that blocks such
events unconditionally in armpmu_event_init(). Instead a quick probe can be
initiated via arm_pmu_branch_stack_supported() to ascertain the support.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
drivers/perf/arm_pmu.c | 3 +--
include/linux/perf/arm_pmu.h | 9 +++++++++
2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index 14a3ed3bdb0b..a85b2d67022e 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -510,8 +510,7 @@ static int armpmu_event_init(struct perf_event *event)
!cpumask_test_cpu(event->cpu, &armpmu->supported_cpus))
return -ENOENT;

- /* does not support taken branch sampling */
- if (has_branch_stack(event))
+ if (has_branch_stack(event) && !arm_pmu_branch_stack_supported(armpmu))
return -EOPNOTSUPP;

return __hw_perf_event_init(event);
diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
index 2a9d07cee927..64e1b2594025 100644
--- a/include/linux/perf/arm_pmu.h
+++ b/include/linux/perf/arm_pmu.h
@@ -80,11 +80,14 @@ enum armpmu_attr_groups {
ARMPMU_NR_ATTR_GROUPS
};

+#define ARM_PMU_BRANCH_STACK BIT(0)
+
struct arm_pmu {
struct pmu pmu;
cpumask_t supported_cpus;
char *name;
int pmuver;
+ int features;
irqreturn_t (*handle_irq)(struct arm_pmu *pmu);
void (*enable)(struct perf_event *event);
void (*disable)(struct perf_event *event);
@@ -119,8 +122,14 @@ struct arm_pmu {

/* Only to be used by ACPI probing code */
unsigned long acpi_cpuid;
+ void *private;
};

+static inline bool arm_pmu_branch_stack_supported(struct arm_pmu *armpmu)
+{
+ return armpmu->features & ARM_PMU_BRANCH_STACK;
+}
+
#define to_arm_pmu(p) (container_of(p, struct arm_pmu, pmu))

u64 armpmu_event_update(struct perf_event *event);
--
2.25.1