[PATCH V2 4/8] perf/x86/intel: Support per thread RDPMC TopDown metrics

kan.liang
2019-06-19T19:22:55Z

With Icelake CPUs, the TopDown metrics are directly available as fixed
counters and do not require generic counters, which make it possible to
measure TopDown per thread/process instead of only per core.

The metrics and slots values have to be saved/restored during context
switching.
The saved values are also used as previous values to calculate the
delta.

The PERF_METRICS MSR value will be returned if RDPMC metrics events.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
---

New for V2

arch/x86/events/core.c | 5 ++-
arch/x86/events/intel/core.c | 101 +++++++++++++++++++++++++++++++++++--------
include/linux/perf_event.h | 3 ++
3 files changed, 90 insertions(+), 19 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 6169af6bf723..fde44fdba256 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2150,7 +2150,10 @@ static int x86_pmu_event_idx(struct perf_event *event)
if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED))
return 0;

- if (x86_pmu.num_counters_fixed && idx >= INTEL_PMC_IDX_FIXED) {
+ /* Return PERF_METRICS MSR value for metrics event */
+ if (is_metric_idx(idx))
+ idx = 1 << 29;
+ else if (x86_pmu.num_counters_fixed && idx >= INTEL_PMC_IDX_FIXED) {
idx -= INTEL_PMC_IDX_FIXED;
idx |= 1 << 30;
}
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 753a345a1db0..1c0dd95fd0d2 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2254,6 +2254,11 @@ static int icl_set_topdown_event_period(struct perf_event *event)
local64_set(&hwc->period_left, 0);
}

+ if ((hwc->saved_slots) && is_first_topdown_event_in_group(event)) {
+ wrmsrl(MSR_CORE_PERF_FIXED_CTR3, hwc->saved_slots);
+ wrmsrl(MSR_PERF_METRICS, hwc->saved_metric);
+ }
+
perf_event_update_userpage(event);

return 0;
@@ -2272,7 +2277,7 @@ static u64 icl_get_metrics_event_value(u64 metric, u64 slots, int idx)
return mul_u64_u32_div(slots, val, 0xff);
}

-static void __icl_update_topdown_event(struct perf_event *event,
+static u64 icl_get_topdown_value(struct perf_event *event,
u64 slots, u64 metrics)
{
int idx = event->hw.idx;
@@ -2283,7 +2288,50 @@ static void __icl_update_topdown_event(struct perf_event *event,
else
delta = slots;

- local64_add(delta, &event->count);
+ return delta;
+}
+
+static void __icl_update_topdown_event(struct perf_event *event,
+ u64 slots, u64 metrics,
+ u64 last_slots, u64 last_metrics)
+{
+ u64 delta, last = 0;
+
+ delta = icl_get_topdown_value(event, slots, metrics);
+ if (last_slots)
+ last = icl_get_topdown_value(event, last_slots, last_metrics);
+
+ /*
+ * The 8bit integer percentage of metric may be not accurate,
+ * especially when the changes is very small.
+ * For example, if only a few bad_spec happens, the percentage
+ * may be reduced from 1% to 0%. If so, the bad_spec event value
+ * will be 0 which is definitely less than the last value.
+ * Avoid update event->count for this case.
+ */
+ if (delta > last) {
+ delta -= last;
+ local64_add(delta, &event->count);
+ }
+}
+
+static void update_saved_topdown_regs(struct perf_event *event,
+ u64 slots, u64 metrics)
+{
+ struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+ struct perf_event *other;
+ int idx;
+
+ event->hw.saved_slots = slots;
+ event->hw.saved_metric = metrics;
+
+ for_each_set_bit(idx, cpuc->active_mask, INTEL_PMC_IDX_TD_BE_BOUND + 1) {
+ if (!is_topdown_idx(idx))
+ continue;
+ other = cpuc->events[idx];
+ other->hw.saved_slots = slots;
+ other->hw.saved_metric = metrics;
+ }
}

/*
@@ -2295,6 +2343,7 @@ static u64 icl_update_topdown_event(struct perf_event *event)
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
struct perf_event *other;
u64 slots, metrics;
+ bool reset = true;
int idx;

/*
@@ -2316,26 +2365,45 @@ static u64 icl_update_topdown_event(struct perf_event *event)
if (!is_topdown_idx(idx))
continue;
other = cpuc->events[idx];
- __icl_update_topdown_event(other, slots, metrics);
+ __icl_update_topdown_event(other, slots, metrics,
+ event ? event->hw.saved_slots : 0,
+ event ? event->hw.saved_metric : 0);
}

/*
* Check and update this event, which may have been cleared
* in active_mask e.g. x86_pmu_stop()
*/
- if (event && !test_bit(event->hw.idx, cpuc->active_mask))
- __icl_update_topdown_event(event, slots, metrics);
+ if (event && !test_bit(event->hw.idx, cpuc->active_mask)) {
+ __icl_update_topdown_event(event, slots, metrics,
+ event->hw.saved_slots,
+ event->hw.saved_metric);

- /*
- * To avoid the known issues as below, the PERF_METRICS and
- * Fixed counter 3 are reset for each read.
- * - The 8bit metrics ratio values lose precision when the
- * measurement period gets longer.
- * - The PERF_METRICS may report wrong value if its delta was
- * less than 1/255 of Fixed counter 3.
- */
- wrmsrl(MSR_PERF_METRICS, 0);
- wrmsrl(MSR_CORE_PERF_FIXED_CTR3, 0);
+ /*
+ * In x86_pmu_stop(), the event is cleared in active_mask first,
+ * then drain the delta, which indicates context switch for
+ * counting.
+ * Save metric and slots for context switch.
+ * Don't need to reset the PERF_METRICS and Fixed counter 3.
+ * Because the values will be restored in next schedule in.
+ */
+ update_saved_topdown_regs(event, slots, metrics);
+ reset = false;
+ }
+
+ if (reset) {
+ /*
+ * To avoid the known issues as below, the PERF_METRICS and
+ * Fixed counter 3 are reset for each read.
+ * - The 8bit metrics ratio values lose precision when the
+ * measurement period gets longer.
+ * - The PERF_METRICS may report wrong value if its delta was
+ * less than 1/255 of Fixed counter 3.
+ */
+ wrmsrl(MSR_PERF_METRICS, 0);
+ wrmsrl(MSR_CORE_PERF_FIXED_CTR3, 0);
+ update_saved_topdown_regs(event, 0, 0);
+ }

return slots;
}
@@ -3517,9 +3585,6 @@ static int intel_pmu_hw_config(struct perf_event *event)
event->attr.config1 = event->hw.config &
X86_ALL_EVENT_FLAGS;
event->hw.flags |= PERF_X86_EVENT_TOPDOWN;
-
- if (is_metric_event(event))
- event->hw.flags &= ~PERF_X86_EVENT_RDPMC_ALLOWED;
}
}

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 3dc01cf98e16..afd53e46d5e6 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -133,6 +133,9 @@ struct hw_perf_event {

struct hw_perf_event_extra extra_reg;
struct hw_perf_event_extra branch_reg;
+
+ u64 saved_slots;
+ u64 saved_metric;
};
struct { /* software */
struct hrtimer hrtimer;
--
2.14.5