linux-kernel - [PATCH V2 10/12] perf intel-pt: Better 7-byte timestamp wraparound logic

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Date:   Fri, 30 Apr 2021 10:03:07 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Andi Kleen <ak@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH V2 10/12] 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@...el.com>
---
 tools/perf/util/intel-pt-decoder/intel-pt-decoder.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

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 7c93ae2bd56c..c4044bc2fb86 100644
--- 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;
-- 
2.25.1