linux-kernel - [PATCH 4.9 108/118] perf intel-pt: Fix CYC timestamp calculation after OVF

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Message-Id: <20190322111223.957271731@linuxfoundation.org>
Date:   Fri, 22 Mar 2019 12:16:20 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Adrian Hunter <adrian.hunter@...el.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 4.9 108/118] perf intel-pt: Fix CYC timestamp calculation after OVF

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Adrian Hunter <adrian.hunter@...el.com>

commit 03997612904866abe7cdcc992784ef65cb3a4b81 upstream.

CYC packet timestamp calculation depends upon CBR which was being
cleared upon overflow (OVF). That can cause errors due to failing to
synchronize with sideband events. Even if a CBR change has been lost,
the old CBR is still a better estimate than zero. So remove the clearing
of CBR.

Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: stable@...r.kernel.org
Link: http://lkml.kernel.org/r/20190206103947.15750-4-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 tools/perf/util/intel-pt-decoder/intel-pt-decoder.c |    1 -
 1 file changed, 1 deletion(-)

--- a/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
+++ b/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
@@ -1311,7 +1311,6 @@ static int intel_pt_overflow(struct inte
 {
 	intel_pt_log("ERROR: Buffer overflow\n");
 	intel_pt_clear_tx_flags(decoder);
-	decoder->cbr = 0;
 	decoder->timestamp_insn_cnt = 0;
 	decoder->pkt_state = INTEL_PT_STATE_ERR_RESYNC;
 	decoder->overflow = true;