perf intel-pt: Do not use TSC packets for calculating CPU cycles to TSC

CBR (core-to-bus ratio) packets provide an indication of CPU frequency. A
more accurate measure can be made by counting the cycles (given by CYC
packets) in between other timing packets (either MTC or TSC). Using TSC
packets has at least 2 issues: 1) timing might have stopped (e.g. mwait) or
2) TSC packets within PSB+ might slip past CYC packets. For now, simply do
not use TSC packets for calculating CPU cycles to TSC. That leaves the case
where 2 MTC packets are used, otherwise falling back to the CBR value.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Link: http://lkml.kernel.org/r/1495786658-18063-37-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 14 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 5dea06289db5..aa1593ce551d 100644
--- a/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
+++ b/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
@@ -711,6 +711,12 @@ static int intel_pt_calc_cyc_cb(struct intel_pt_pkt_info *pkt_info)
                 break;
 
         case INTEL_PT_TSC:
+                /*
+                 * For now, do not support using TSC packets - refer
+                 * intel_pt_calc_cyc_to_tsc().
+                 */
+                if (data->from_mtc)
+                        return 1;
                 timestamp = pkt_info->packet.payload |
                             (data->timestamp & (0xffULL << 56));
                 if (data->from_mtc && timestamp < data->timestamp &&
@@ -828,6 +834,14 @@ static void intel_pt_calc_cyc_to_tsc(struct intel_pt_decoder *decoder,
                 .cbr_cyc_to_tsc = 0,
         };
 
+        /*
+         * For now, do not support using TSC packets for at least the reasons:
+         * 1) timing might have stopped
+         * 2) TSC packets within PSB+ can slip against CYC packets
+         */
+        if (!from_mtc)
+                return;
+
         intel_pt_pkt_lookahead(decoder, intel_pt_calc_cyc_cb, &data);
 }