perf intel-pt: Better 7-byte timestamp wraparound logic

A timestamp should not go backwards. If it does it is assumed that the
 7-byte TSC packet value has wrapped. Improve that logic so that it will
not allow the timestamp to go past the buffer timestamp (which is recorded
when the buffer is copied out)

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20210430070309.17624-11-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c b/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
index 7c93ae2..c4044bc 100644 (file)
--- a/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
+++ b/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
@@ -1499,9 +1499,15 @@ static void intel_pt_calc_tsc_timestamp(struct intel_pt_decoder *decoder)
                        timestamp = decoder->timestamp;
                }
                if (timestamp < decoder->timestamp) {
-                       intel_pt_log_to("Wraparound timestamp", timestamp);
-                       timestamp += (1ULL << 56);
-                       decoder->tsc_timestamp = timestamp;
+                       if (!decoder->buf_timestamp ||
+                           (timestamp + (1ULL << 56) < decoder->buf_timestamp)) {
+                               intel_pt_log_to("Wraparound timestamp", timestamp);
+                               timestamp += (1ULL << 56);
+                               decoder->tsc_timestamp = timestamp;
+                       } else {
+                               intel_pt_log_to("Suppressing bad timestamp", timestamp);
+                               timestamp = decoder->timestamp;
+                       }
                }
                decoder->timestamp = timestamp;
                decoder->timestamp_insn_cnt = 0;