[PATCH V12 07/10] arm64/perf: Add PERF_ATTACH_TASK_DATA to events with has_branch_stack()

[Anshuman Khandual]

Short running processes i.e those getting very small cpu run time each time
when they get scheduled on, might not accumulate much branch records before
a PMU IRQ really happens. This increases possibility, for such processes to
loose much of its branch records, while being scheduled in-out of various
cpus on the system.

There is a need to save all occurred branch records during the cpu run time
while the process gets scheduled out. It requires an event context specific
buffer for such storage.

This adds PERF_ATTACH_TASK_DATA flag unconditionally, for all branch stack
sampling events, which would allocate task_ctx_data during its event init.
This also creates a platform specific task_ctx_data kmem cache which will
serve such allocation requests.

This adds a new structure 'arm64_perf_task_context' which encapsulates brbe
register set for maximum possible BRBE entries on the HW along with a valid
records tracking element.

Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Tested-by: James Clark <james.clark@xxxxxxx>
Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
---
 arch/arm64/include/asm/perf_event.h |  4 ++++
 drivers/perf/arm_brbe.c             | 21 +++++++++++++++++++++
 drivers/perf/arm_brbe.h             | 13 +++++++++++++
 drivers/perf/arm_pmuv3.c            | 16 +++++++++++++---
 4 files changed, 51 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/perf_event.h b/arch/arm64/include/asm/perf_event.h
index 49a973571415..b0c12a5882df 100644
--- a/arch/arm64/include/asm/perf_event.h
+++ b/arch/arm64/include/asm/perf_event.h
@@ -38,6 +38,8 @@ void armv8pmu_branch_enable(struct perf_event *event);
 void armv8pmu_branch_disable(struct perf_event *event);
 void armv8pmu_branch_probe(struct arm_pmu *arm_pmu);
 void armv8pmu_branch_reset(void);
+int armv8pmu_task_ctx_cache_alloc(struct arm_pmu *arm_pmu);
+void armv8pmu_task_ctx_cache_free(struct arm_pmu *arm_pmu);
 #else
 static inline void armv8pmu_branch_read(struct pmu_hw_events *cpuc, struct perf_event *event)
 {
@@ -62,6 +64,8 @@ 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) { }
+static inline int armv8pmu_task_ctx_cache_alloc(struct arm_pmu *arm_pmu) { return 0; }
+static inline void armv8pmu_task_ctx_cache_free(struct arm_pmu *arm_pmu) { }
 #endif
 #endif
 #endif
diff --git a/drivers/perf/arm_brbe.c b/drivers/perf/arm_brbe.c
index 90bc9131223d..4729cb49282b 100644
--- a/drivers/perf/arm_brbe.c
+++ b/drivers/perf/arm_brbe.c
@@ -109,6 +109,27 @@ bool armv8pmu_branch_attr_valid(struct perf_event *event)
 	return true;
 }
 
+static inline struct kmem_cache *
+arm64_create_brbe_task_ctx_kmem_cache(size_t size)
+{
+	return kmem_cache_create("arm64_brbe_task_ctx", size, 0, 0, NULL);
+}
+
+int armv8pmu_task_ctx_cache_alloc(struct arm_pmu *arm_pmu)
+{
+	size_t size = sizeof(struct arm64_perf_task_context);
+
+	arm_pmu->pmu.task_ctx_cache = arm64_create_brbe_task_ctx_kmem_cache(size);
+	if (!arm_pmu->pmu.task_ctx_cache)
+		return -ENOMEM;
+	return 0;
+}
+
+void armv8pmu_task_ctx_cache_free(struct arm_pmu *arm_pmu)
+{
+	kmem_cache_destroy(arm_pmu->pmu.task_ctx_cache);
+}
+
 static int brbe_attributes_probe(struct arm_pmu *armpmu, u32 brbe)
 {
 	u64 brbidr = read_sysreg_s(SYS_BRBIDR0_EL1);
diff --git a/drivers/perf/arm_brbe.h b/drivers/perf/arm_brbe.h
index a47480eec070..4a72c2ba7140 100644
--- a/drivers/perf/arm_brbe.h
+++ b/drivers/perf/arm_brbe.h
@@ -80,12 +80,25 @@
  *	---------------------------------	------
  */
 #define BRBE_BANK_MAX_ENTRIES 32
+#define BRBE_MAX_BANK 2
+#define BRBE_MAX_ENTRIES (BRBE_BANK_MAX_ENTRIES * BRBE_MAX_BANK)
 
 #define BRBE_BANK0_IDX_MIN 0
 #define BRBE_BANK0_IDX_MAX 31
 #define BRBE_BANK1_IDX_MIN 32
 #define BRBE_BANK1_IDX_MAX 63
 
+struct brbe_regset {
+	unsigned long brbsrc;
+	unsigned long brbtgt;
+	unsigned long brbinf;
+};
+
+struct arm64_perf_task_context {
+	struct brbe_regset store[BRBE_MAX_ENTRIES];
+	int nr_brbe_records;
+};
+
 struct brbe_hw_attr {
 	int	brbe_version;
 	int	brbe_cc;
diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
index 02907371523a..3c079051a63a 100644
--- a/drivers/perf/arm_pmuv3.c
+++ b/drivers/perf/arm_pmuv3.c
@@ -1022,8 +1022,12 @@ static int __armv8_pmuv3_map_event(struct perf_event *event,
 
 	hw_event_id = __armv8_pmuv3_map_event_id(armpmu, event);
 
-	if (has_branch_stack(event) && !armv8pmu_branch_attr_valid(event))
-		return -EOPNOTSUPP;
+	if (has_branch_stack(event)) {
+		if (!armv8pmu_branch_attr_valid(event))
+			return -EOPNOTSUPP;
+
+		event->attach_state |= PERF_ATTACH_TASK_DATA;
+	}
 
 	/*
 	 * CHAIN events only work when paired with an adjacent counter, and it
@@ -1188,9 +1192,15 @@ static int armv8pmu_probe_pmu(struct arm_pmu *cpu_pmu)
 		return -ENODEV;
 
 	if (cpu_pmu->has_branch_stack) {
-		ret = branch_records_alloc(cpu_pmu);
+		ret = armv8pmu_task_ctx_cache_alloc(cpu_pmu);
 		if (ret)
 			return ret;
+
+		ret = branch_records_alloc(cpu_pmu);
+		if (ret) {
+			armv8pmu_task_ctx_cache_free(cpu_pmu);
+			return ret;
+		}
 	}
 	return 0;
 }
-- 
2.25.1