[PATCH V7 5/6] arm64/perf: Add branch stack support in ARMV8 PMU

Anshuman Khandual
2023-01-05T18:54:32Z

This enables support for branch stack sampling event in ARMV8 PMU, checking
has_branch_stack() on the event inside 'struct arm_pmu' callbacks. Although
these branch stack helpers armv8pmu_branch_XXXXX() are just dummy functions
for now. While here, this also defines arm_pmu's sched_task() callback with
armv8pmu_sched_task(), which resets the branch record buffer on a sched_in.

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>
---
arch/arm64/include/asm/perf_event.h | 10 +++++++++
arch/arm64/kernel/perf_event.c | 35 +++++++++++++++++++++++++++++
2 files changed, 45 insertions(+)

diff --git a/arch/arm64/include/asm/perf_event.h b/arch/arm64/include/asm/perf_event.h
index 3eaf462f5752..a038902d6874 100644
--- a/arch/arm64/include/asm/perf_event.h
+++ b/arch/arm64/include/asm/perf_event.h
@@ -273,4 +273,14 @@ extern unsigned long perf_misc_flags(struct pt_regs *regs);
(regs)->pstate = PSR_MODE_EL1h; \
}

+struct pmu_hw_events;
+struct arm_pmu;
+struct perf_event;
+
+static inline void armv8pmu_branch_read(struct pmu_hw_events *cpuc, struct perf_event *event) { }
+static inline bool armv8pmu_branch_valid(struct perf_event *event) { return false; }
+static inline void armv8pmu_branch_enable(struct perf_event *event) { }
+static inline void armv8pmu_branch_disable(struct perf_event *event) { }
+static inline void armv8pmu_branch_probe(struct arm_pmu *arm_pmu) { }
+static inline void armv8pmu_branch_reset(void) { }
#endif
diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index a5193f2146a6..8805b4516088 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -789,10 +789,22 @@ static void armv8pmu_enable_event(struct perf_event *event)
* Enable counter
*/
armv8pmu_enable_event_counter(event);
+
+ /*
+ * Enable BRBE
+ */
+ if (has_branch_stack(event))
+ armv8pmu_branch_enable(event);
}

static void armv8pmu_disable_event(struct perf_event *event)
{
+ /*
+ * Disable BRBE
+ */
+ if (has_branch_stack(event))
+ armv8pmu_branch_disable(event);
+
/*
* Disable counter
*/
@@ -878,6 +890,13 @@ static irqreturn_t armv8pmu_handle_irq(struct arm_pmu *cpu_pmu)
if (!armpmu_event_set_period(event))
continue;

+ if (has_branch_stack(event)) {
+ WARN_ON(!cpuc->branches);
+ armv8pmu_branch_read(cpuc, event);
+ data.br_stack = &cpuc->branches->branch_stack;
+ data.sample_flags |= PERF_SAMPLE_BRANCH_STACK;
+ }
+
/*
* Perf event overflow will queue the processing of the event as
* an irq_work which will be taken care of in the handling of
@@ -976,6 +995,14 @@ static int armv8pmu_user_event_idx(struct perf_event *event)
return event->hw.idx;
}

+static void armv8pmu_sched_task(struct perf_event_pmu_context *pmu_ctx, bool sched_in)
+{
+ struct arm_pmu *armpmu = to_arm_pmu(pmu_ctx->pmu);
+
+ if (sched_in && arm_pmu_branch_stack_supported(armpmu))
+ armv8pmu_branch_reset();
+}
+
/*
* Add an event filter to a given event.
*/
@@ -1052,6 +1079,9 @@ static void armv8pmu_reset(void *info)
pmcr |= ARMV8_PMU_PMCR_LP;

armv8pmu_pmcr_write(pmcr);
+
+ if (arm_pmu_branch_stack_supported(cpu_pmu))
+ armv8pmu_branch_reset();
}

static int __armv8_pmuv3_map_event(struct perf_event *event,
@@ -1069,6 +1099,9 @@ static int __armv8_pmuv3_map_event(struct perf_event *event,
&armv8_pmuv3_perf_cache_map,
ARMV8_PMU_EVTYPE_EVENT);

+ if (has_branch_stack(event) && !armv8pmu_branch_valid(event))
+ return -EOPNOTSUPP;
+
if (armv8pmu_event_is_64bit(event))
event->hw.flags |= ARMPMU_EVT_64BIT;

@@ -1181,6 +1214,7 @@ static void __armv8pmu_probe_pmu(void *info)
cpu_pmu->reg_pmmir = read_cpuid(PMMIR_EL1);
else
cpu_pmu->reg_pmmir = 0;
+ armv8pmu_branch_probe(cpu_pmu);
}

static int armv8pmu_probe_pmu(struct arm_pmu *cpu_pmu)
@@ -1261,6 +1295,7 @@ static int armv8_pmu_init(struct arm_pmu *cpu_pmu, char *name,
cpu_pmu->filter = armv8pmu_filter;

cpu_pmu->pmu.event_idx = armv8pmu_user_event_idx;
+ cpu_pmu->sched_task = armv8pmu_sched_task;

cpu_pmu->name = name;
cpu_pmu->map_event = map_event;
--
2.25.1