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@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: stable@vger.kernel.org # v4.3+
Link: http://lkml.kernel.org/r/1475062896-22274-2-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 36 insertions, 0 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 3d1d446f037f..16c06d3ae577 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