[tip:perf/urgent] perf intel-pt: Fix MTC timestamp calculation for large MTC periods

From: tip-bot for Adrian Hunter
Date: Thu Oct 06 2016 - 18:41:16 EST


Commit-ID: 3bccbe20f6d188ce7b00326e776b745cfd35b10a
Gitweb: http://git.kernel.org/tip/3bccbe20f6d188ce7b00326e776b745cfd35b10a
Author: Adrian Hunter <adrian.hunter@xxxxxxxxx>
AuthorDate: Wed, 28 Sep 2016 14:41:36 +0300
Committer: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Wed, 5 Oct 2016 08:15:58 -0300

perf intel-pt: Fix MTC timestamp calculation for large MTC periods

The MTC packet provides a 8-bit slice of CTC which is related to TSC by
the TMA packet, however the TMA packet only provides the lower 16 bits
of CTC. If mtc_shift > 8 then some of the MTC bits are not in the CTC
provided by the TMA packet. Fix-up the last_mtc calculated from the TMA
packet by copying the missing bits from the current MTC assuming the
least difference between the two, and that the current MTC comes after
last_mtc.

Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v4.3+
Link: http://lkml.kernel.org/r/1475062896-22274-2-git-send-email-adrian.hunter@xxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
.../perf/util/intel-pt-decoder/intel-pt-decoder.c | 36 ++++++++++++++++++++++
1 file changed, 36 insertions(+)

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 3d1d446..16c06d3 100644
--- a/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
+++ b/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
@@ -90,6 +90,7 @@ struct intel_pt_decoder {
bool pge;
bool have_tma;
bool have_cyc;
+ bool fixup_last_mtc;
uint64_t pos;
uint64_t last_ip;
uint64_t ip;
@@ -586,10 +587,31 @@ struct intel_pt_calc_cyc_to_tsc_info {
uint64_t tsc_timestamp;
uint64_t timestamp;
bool have_tma;
+ bool fixup_last_mtc;
bool from_mtc;
double cbr_cyc_to_tsc;
};

+/*
+ * MTC provides a 8-bit slice of CTC but the TMA packet only provides the lower
+ * 16 bits of CTC. If mtc_shift > 8 then some of the MTC bits are not in the CTC
+ * provided by the TMA packet. Fix-up the last_mtc calculated from the TMA
+ * packet by copying the missing bits from the current MTC assuming the least
+ * difference between the two, and that the current MTC comes after last_mtc.
+ */
+static void intel_pt_fixup_last_mtc(uint32_t mtc, int mtc_shift,
+ uint32_t *last_mtc)
+{
+ uint32_t first_missing_bit = 1U << (16 - mtc_shift);
+ uint32_t mask = ~(first_missing_bit - 1);
+
+ *last_mtc |= mtc & mask;
+ if (*last_mtc >= mtc) {
+ *last_mtc -= first_missing_bit;
+ *last_mtc &= 0xff;
+ }
+}
+
static int intel_pt_calc_cyc_cb(struct intel_pt_pkt_info *pkt_info)
{
struct intel_pt_decoder *decoder = pkt_info->decoder;
@@ -619,6 +641,11 @@ static int intel_pt_calc_cyc_cb(struct intel_pt_pkt_info *pkt_info)
return 0;

mtc = pkt_info->packet.payload;
+ if (decoder->mtc_shift > 8 && data->fixup_last_mtc) {
+ data->fixup_last_mtc = false;
+ intel_pt_fixup_last_mtc(mtc, decoder->mtc_shift,
+ &data->last_mtc);
+ }
if (mtc > data->last_mtc)
mtc_delta = mtc - data->last_mtc;
else
@@ -687,6 +714,7 @@ static int intel_pt_calc_cyc_cb(struct intel_pt_pkt_info *pkt_info)

data->ctc_delta = 0;
data->have_tma = true;
+ data->fixup_last_mtc = true;

return 0;

@@ -753,6 +781,7 @@ static void intel_pt_calc_cyc_to_tsc(struct intel_pt_decoder *decoder,
.tsc_timestamp = decoder->tsc_timestamp,
.timestamp = decoder->timestamp,
.have_tma = decoder->have_tma,
+ .fixup_last_mtc = decoder->fixup_last_mtc,
.from_mtc = from_mtc,
.cbr_cyc_to_tsc = 0,
};
@@ -1271,6 +1300,7 @@ static void intel_pt_calc_tma(struct intel_pt_decoder *decoder)
}
decoder->ctc_delta = 0;
decoder->have_tma = true;
+ decoder->fixup_last_mtc = true;
intel_pt_log("CTC timestamp " x64_fmt " last MTC %#x CTC rem %#x\n",
decoder->ctc_timestamp, decoder->last_mtc, ctc_rem);
}
@@ -1285,6 +1315,12 @@ static void intel_pt_calc_mtc_timestamp(struct intel_pt_decoder *decoder)

mtc = decoder->packet.payload;

+ if (decoder->mtc_shift > 8 && decoder->fixup_last_mtc) {
+ decoder->fixup_last_mtc = false;
+ intel_pt_fixup_last_mtc(mtc, decoder->mtc_shift,
+ &decoder->last_mtc);
+ }
+
if (mtc > decoder->last_mtc)
mtc_delta = mtc - decoder->last_mtc;
else