path: root/drivers/hwtracing
diff options
authorSuzuki K Poulose <>2021-04-05 17:42:56 +0100
committerMathieu Poirier <>2021-04-06 16:05:37 -0600
commit0e6c205175969a7ef5a7689844b0f889728d3be2 (patch)
treeffebbf50403dd9cd25898218474484c77b85b30a /drivers/hwtracing
parent8b4811965f53251b89af8654291e965047367b25 (diff)
coresight: etm-perf: Allow an event to use different sinks
When a sink is not specified by the user, the etm perf driver finds a suitable sink automatically, based on the first ETM where this event could be scheduled. Then we allocate the sink buffer based on the selected sink. This is fine for a CPU bound event as the "sink" is always guaranteed to be reachable from the ETM (as this is the only ETM where the event is going to be scheduled). However, if we have a thread bound event, the event could be scheduled on any of the ETMs on the system. In this case, currently we automatically select a sink and exclude any ETMs that cannot reach the selected sink. This is problematic especially for 1x1 configurations. We end up in tracing the event only on the "first" ETM, as the default sink is local to the first ETM and unreachable from the rest. However, we could allow the other ETMs to trace if they all have a sink that is compatible with the "selected" sink and can use the sink buffer. This can be easily done by verifying that they are all driven by the same driver and matches the same subtype. Please note that at anytime there can be only one ETM tracing the event. Adding support for different types of sinks for a single event is complex and is not something that we expect on a sane configuration. Cc: Anshuman Khandual <> Reviewed-by: Mike Leach <> Tested-by: Linu Cherian <> Signed-off-by: Suzuki K Poulose <> Link: Signed-off-by: Mathieu Poirier <>
Diffstat (limited to 'drivers/hwtracing')
1 files changed, 52 insertions, 8 deletions
diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
index 0f603b4094f2..aa0974bd265b 100644
--- a/drivers/hwtracing/coresight/coresight-etm-perf.c
+++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
@@ -232,6 +232,25 @@ static void etm_free_aux(void *data)
+ * Check if two given sinks are compatible with each other,
+ * so that they can use the same sink buffers, when an event
+ * moves around.
+ */
+static bool sinks_compatible(struct coresight_device *a,
+ struct coresight_device *b)
+ if (!a || !b)
+ return false;
+ /*
+ * If the sinks are of the same subtype and driven
+ * by the same driver, we can use the same buffer
+ * on these sinks.
+ */
+ return (a->subtype.sink_subtype == b->subtype.sink_subtype) &&
+ (sink_ops(a) == sink_ops(b));
static void *etm_setup_aux(struct perf_event *event, void **pages,
int nr_pages, bool overwrite)
@@ -239,6 +258,7 @@ static void *etm_setup_aux(struct perf_event *event, void **pages,
int cpu = event->cpu;
cpumask_t *mask;
struct coresight_device *sink = NULL;
+ struct coresight_device *user_sink = NULL, *last_sink = NULL;
struct etm_event_data *event_data = NULL;
event_data = alloc_event_data(cpu);
@@ -249,7 +269,7 @@ static void *etm_setup_aux(struct perf_event *event, void **pages,
/* First get the selected sink from user space. */
if (event->attr.config2) {
id = (u32)event->attr.config2;
- sink = coresight_get_sink_by_id(id);
+ sink = user_sink = coresight_get_sink_by_id(id);
mask = &event_data->mask;
@@ -277,14 +297,33 @@ static void *etm_setup_aux(struct perf_event *event, void **pages,
- * No sink provided - look for a default sink for one of the
- * devices. At present we only support topology where all CPUs
- * use the same sink [N:1], so only need to find one sink. The
- * coresight_build_path later will remove any CPU that does not
- * attach to the sink, or if we have not found a sink.
+ * No sink provided - look for a default sink for all the ETMs,
+ * where this event can be scheduled.
+ * We allocate the sink specific buffers only once for this
+ * event. If the ETMs have different default sink devices, we
+ * can only use a single "type" of sink as the event can carry
+ * only one sink specific buffer. Thus we have to make sure
+ * that the sinks are of the same type and driven by the same
+ * driver, as the one we allocate the buffer for. As such
+ * we choose the first sink and check if the remaining ETMs
+ * have a compatible default sink. We don't trace on a CPU
+ * if the sink is not compatible.
- if (!sink)
+ if (!user_sink) {
+ /* Find the default sink for this ETM */
sink = coresight_find_default_sink(csdev);
+ if (!sink) {
+ cpumask_clear_cpu(cpu, mask);
+ continue;
+ }
+ /* Check if this sink compatible with the last sink */
+ if (last_sink && !sinks_compatible(last_sink, sink)) {
+ cpumask_clear_cpu(cpu, mask);
+ continue;
+ }
+ last_sink = sink;
+ }
* Building a path doesn't enable it, it simply builds a
@@ -312,7 +351,12 @@ static void *etm_setup_aux(struct perf_event *event, void **pages,
if (!sink_ops(sink)->alloc_buffer || !sink_ops(sink)->free_buffer)
goto err;
- /* Allocate the sink buffer for this session */
+ /*
+ * Allocate the sink buffer for this session. All the sinks
+ * where this event can be scheduled are ensured to be of the
+ * same type. Thus the same sink configuration is used by the
+ * sinks.
+ */
event_data->snk_config =
sink_ops(sink)->alloc_buffer(sink, event, pages,
nr_pages, overwrite);