[PATCH 31/35] perf intel-pt: Disable sync switch with guest sideband

Adrian Hunter
2022-07-11T10:15:03Z

The sync_switch facility attempts to better synchronize context switches
with the Intel PT trace, however it is not designed for guest machine
context switches, so disable it when guest sideband is detected.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
tools/perf/util/intel-pt.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)

diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c
index 98b097fec476..dc2af64f9e31 100644
--- a/tools/perf/util/intel-pt.c
+++ b/tools/perf/util/intel-pt.c
@@ -74,6 +74,7 @@ struct intel_pt {
bool data_queued;
bool est_tsc;
bool sync_switch;
+ bool sync_switch_not_supported;
bool mispred_all;
bool use_thread_stack;
bool callstack;
@@ -2638,6 +2639,9 @@ static void intel_pt_enable_sync_switch(struct intel_pt *pt)
{
unsigned int i;

+ if (pt->sync_switch_not_supported)
+ return;
+
pt->sync_switch = true;

for (i = 0; i < pt->queues.nr_queues; i++) {
@@ -2649,6 +2653,23 @@ static void intel_pt_enable_sync_switch(struct intel_pt *pt)
}
}

+static void intel_pt_disable_sync_switch(struct intel_pt *pt)
+{
+ unsigned int i;
+
+ pt->sync_switch = false;
+
+ for (i = 0; i < pt->queues.nr_queues; i++) {
+ struct auxtrace_queue *queue = &pt->queues.queue_array[i];
+ struct intel_pt_queue *ptq = queue->priv;
+
+ if (ptq) {
+ ptq->sync_switch = false;
+ intel_pt_next_tid(pt, ptq);
+ }
+ }
+}
+
/*
* To filter against time ranges, it is only necessary to look at the next start
* or end time.
@@ -3090,6 +3111,14 @@ static int intel_pt_guest_context_switch(struct intel_pt *pt,

pt->have_guest_sideband = true;

+ /*
+ * sync_switch cannot handle guest machines at present, so just disable
+ * it.
+ */
+ pt->sync_switch_not_supported = true;
+ if (pt->sync_switch)
+ intel_pt_disable_sync_switch(pt);
+
if (out)
return 0;

--
2.25.1