perf: qcom: Add L3 cache PMU driver

This adds a new dynamic PMU to the Perf Events framework to program and control the L3 cache PMUs in some Qualcomm Technologies SOCs.

The driver supports a distributed cache architecture where the overall cache for a socket is comprised of multiple slices each with its own PMU. Access to each individual PMU is provided even though all CPUs share all the slices. User space needs to aggregate to individual counts to provide a global picture.

The driver exports formatting and event information to sysfs so it can be used by the perf user space tools with the syntaxes:

   perf stat -a -e l3cache_0_0/read-miss/
   perf stat -a -e l3cache_0_0/event=0x21/

Signed-off-by Agustin Vega-Frias <[email protected]>

drivers/perf/qcom_l3_pmu.c new file +8 -0

+static int qcom_l3_cache__event_init(struct perf_event *event)
+{
+	struct l3cache_pmu *l3pmu = to_l3cache_pmu(event->pmu);
+	struct hw_perf_event *hwc = &event->hw;
+	struct perf_event *sibling;
 
+	/*
+	 * We must NOT create groups containing mixed PMUs, although software
+	 * events are acceptable

Hi Agustin,

Quoted 12 lines · Agustin Vega-Frias

This adds a new dynamic PMU to the Perf Events framework to program and control the L3 cache PMUs in some Qualcomm Technologies SOCs.

The driver supports a distributed cache architecture where the overall cache for a socket is comprised of multiple slices each with its own PMU.
Access to each individual PMU is provided even though all CPUs share all
the slices. User space needs to aggregate to individual counts to provide
a global picture.

Quoted 6 lines

The driver exports formatting and event information to sysfs so it can be used by the perf user space tools with the syntaxes:

   perf stat -a -e l3cache_0_0/read-miss/
   perf stat -a -e l3cache_0_0/event=0x21/

Signed-off-by Agustin Vega-Frias <[email protected]>

Thanks for respinning this; it looks good to me.

Quoted 10 lines

drivers/perf/qcom_l3_pmu.c new file +7 -0

+static int qcom_l3_cache__event_init(struct perf_event *event)
+{
+	struct l3cache_pmu *l3pmu = to_l3cache_pmu(event->pmu);
+	struct hw_perf_event *hwc = &event->hw;
+	struct perf_event *sibling;
 
+	/*
+	 * We must NOT create groups containing mixed PMUs, although 

software

drivers/perf/qcom_l3_pmu.c new file +1 -0

+	 * events are acceptable

drivers/perf/qcom_l3_pmu.c line 493

Quoted 10 lines

drivers/perf/qcom_l3_pmu.c new file +10 -0

+	 */
+	if (event->group_leader->pmu != event->pmu &&
+			!is_software_event(event->group_leader))
+		return -EINVAL;
+
+	list_for_each_entry(sibling, &event->group_leader->sibling_list,
+			group_entry)
+		if (sibling->pmu != event->pmu &&
+				!is_software_event(sibling))
+			return -EINVAL;

Sorry for spotting this so late, but I just noticed that we don't validate the group isn't too large to ever fit in the HW, which is important for avoiding pointless work in perf_rotate_context() when the mux hrtimer callback occurs.

We fail to do that in other drivers, too, so that's something we should clean up more generally.

Here, I'd like to factor the group validation logic out into a helper:

#define event_num_counters(e) (event_uses_long_counter(e) ? 2 : 1)

static bool qcom_l3_cache__validate_event_group(struct perf_event *event)

{
	struct perf_event *leader = event->group_leader;
	struct perf_event *sibling;
	int counters = 0;

	/*
	 * We must NOT create groups containing mixed PMUs, although
	 * software.
	 */
	if (leader->pmu != event->pmu && !is_software_event(leader))
		return false;

	counters = event_num_counters(event);
	counters += event_num_counters(leader);

	list_for_each_entry(sibling, &leader->sibling_list, group_entry) {
		if (is_software_event(sibling))
			continue;
		if (sibling->pmu != event->pmu)
			return false;
		counters += event_num_counters(sibling);
	}

	/*
	 * If the group requires more counters than the HW has, it
	 * cannot ever be scheduled.
	 */
	return counters <= L3_NUM_COUNTERS;
}

... where in qcom_l3_cache__event_init() we'd do:

	if (!qcom_l3_cache__validate_event_group(event))
		return -EINVAL;

If you're happy with that, I can make that change when applying.