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Subject[PATCH 3/6] arm_pmu: Add support for long event counters
Date
Each PMU has a set of fixed width event counters. But in some
special cases, the events could be counted using a counter which
effectively has twice the normal width of a coutner.
e.g, Arm V8 PMUv3 has a 64 bit cycle counter which can count
only the CPU cylces. Also, the PMU can chain the event counters
to effectively count as a 64bit counter.

Add support for tracking the events that uses double the normal
counter size. This only affects the periods set for each counter.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
drivers/perf/arm_pmu.c | 25 ++++++++++++++++++++++---
include/linux/perf/arm_pmu.h | 6 ++++++
2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index e23e1a1..1adabb5 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -33,6 +33,21 @@ static inline u64 arm_pmu_max_period(struct arm_pmu *pmu)
return (((u64)1) << (pmu->counter_width)) - 1;
}

+static inline u64 arm_pmu_get_event_max_period(struct arm_pmu *pmu,
+ struct perf_event *event)
+{
+ u64 period = arm_pmu_max_period(pmu);
+
+ /*
+ * To prevent shift-counter-overflow warning, create the
+ * mask, by shift + OR sequence.
+ */
+ if (event->hw.flags & ARMPMU_EVT_LONG)
+ period = (period << pmu->counter_width) | period;
+
+ return period;
+}
+
static int
armpmu_map_cache_event(const unsigned (*cache_map)
[PERF_COUNT_HW_CACHE_MAX]
@@ -122,7 +137,7 @@ int armpmu_event_set_period(struct perf_event *event)
u64 max_period;
int ret = 0;

- max_period = arm_pmu_max_period(armpmu);
+ max_period = arm_pmu_get_event_max_period(armpmu, event);
if (unlikely(left <= -period)) {
left = period;
local64_set(&hwc->period_left, left);
@@ -148,7 +163,7 @@ int armpmu_event_set_period(struct perf_event *event)

local64_set(&hwc->prev_count, (u64)-left);

- armpmu->write_counter(event, (u64)(-left) & 0xffffffff);
+ armpmu->write_counter(event, (u64)(-left) & max_period);

perf_event_update_userpage(event);

@@ -160,7 +175,7 @@ u64 armpmu_event_update(struct perf_event *event)
struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
struct hw_perf_event *hwc = &event->hw;
u64 delta, prev_raw_count, new_raw_count;
- u64 max_period = arm_pmu_max_period(armpmu);
+ u64 max_period = arm_pmu_get_event_max_period(armpmu, event);

again:
prev_raw_count = local64_read(&hwc->prev_count);
@@ -368,6 +383,7 @@ __hw_perf_event_init(struct perf_event *event)
struct hw_perf_event *hwc = &event->hw;
int mapping;

+ hwc->flags = 0;
mapping = armpmu->map_event(event);

if (mapping < 0) {
@@ -670,6 +686,9 @@ static void cpu_pm_pmu_setup(struct arm_pmu *armpmu, unsigned long cmd)
continue;

event = hw_events->events[idx];
+ /* Chained events could use multiple counters */
+ if (!event)
+ continue;

switch (cmd) {
case CPU_PM_ENTER:
diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
index 705e8c3..ed7e3f7 100644
--- a/include/linux/perf/arm_pmu.h
+++ b/include/linux/perf/arm_pmu.h
@@ -25,6 +25,12 @@
*/
#define ARMPMU_MAX_HWEVENTS 32

+/*
+ * ARM PMU hw_event flags
+ */
+/* Event uses a counter with double the normal width */
+#define ARMPMU_EVT_LONG 1
+
#define HW_OP_UNSUPPORTED 0xFFFF
#define C(_x) PERF_COUNT_HW_CACHE_##_x
#define CACHE_OP_UNSUPPORTED 0xFFFF
--
2.7.4
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