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Subject[PATCH v3 3/3] perf/x86/intel/pt: Add sampling support
Date
Add AUX sampling support to the PT PMU: implement an NMI-safe callback
that takes a snapshot of the buffer without touching the event states.
This is done for PT events that don't use PMIs, that is, snapshot mode
(RO mapping of the AUX area).

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
---
arch/x86/events/intel/pt.c | 54 ++++++++++++++++++++++++++++++++++++++
1 file changed, 54 insertions(+)

diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index 170f3b402274..2f20d5a333c1 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -1208,6 +1208,13 @@ pt_buffer_setup_aux(struct perf_event *event, void **pages,
if (!nr_pages)
return NULL;

+ /*
+ * Only support AUX sampling in snapshot mode, where we don't
+ * generate NMIs.
+ */
+ if (event->attr.aux_sample_size && !snapshot)
+ return NULL;
+
if (cpu == -1)
cpu = raw_smp_processor_id();
node = cpu_to_node(cpu);
@@ -1506,6 +1513,52 @@ static void pt_event_stop(struct perf_event *event, int mode)
}
}

+static long pt_event_snapshot_aux(struct perf_event *event,
+ struct perf_output_handle *handle,
+ unsigned long size)
+{
+ struct pt *pt = this_cpu_ptr(&pt_ctx);
+ struct pt_buffer *buf = perf_get_aux(&pt->handle);
+ unsigned long from = 0, to;
+ long ret;
+
+ if (WARN_ON_ONCE(!buf))
+ return 0;
+
+ /*
+ * Sampling is only allowed on snapshot events;
+ * see pt_buffer_setup_aux().
+ */
+ if (WARN_ON_ONCE(!buf->snapshot))
+ return 0;
+
+ /*
+ * Here, handle_nmi tells us if the tracing is on
+ */
+ if (READ_ONCE(pt->handle_nmi))
+ pt_config_stop(event);
+
+ pt_read_offset(buf);
+ pt_update_head(pt);
+
+ to = local_read(&buf->data_size);
+ if (to < size)
+ from = buf->nr_pages << PAGE_SHIFT;
+ from += to - size;
+
+ ret = perf_output_copy_aux(&pt->handle, handle, from, to);
+
+ /*
+ * If the tracing was on when we turned up, restart it.
+ * Compiler barrier not needed as we couldn't have been
+ * preempted by anything that touches pt->handle_nmi.
+ */
+ if (pt->handle_nmi)
+ pt_config_start(event);
+
+ return ret;
+}
+
static void pt_event_del(struct perf_event *event, int mode)
{
pt_event_stop(event, PERF_EF_UPDATE);
@@ -1625,6 +1678,7 @@ static __init int pt_init(void)
pt_pmu.pmu.del = pt_event_del;
pt_pmu.pmu.start = pt_event_start;
pt_pmu.pmu.stop = pt_event_stop;
+ pt_pmu.pmu.snapshot_aux = pt_event_snapshot_aux;
pt_pmu.pmu.read = pt_event_read;
pt_pmu.pmu.setup_aux = pt_buffer_setup_aux;
pt_pmu.pmu.free_aux = pt_buffer_free_aux;
--
2.23.0
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