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

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Message-Id: <20210429125854.13905-11-adrian.hunter@intel.com>
Date:   Thu, 29 Apr 2021 15:58:52 +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 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 ba5b5782acc1..b95312ec3832 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;
-- 
2.17.1