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authorAdrian Hunter <adrian.hunter@intel.com>2019-03-25 16:51:35 +0300
committerArnaldo Carvalho de Melo <acme@redhat.com>2019-03-28 20:31:55 +0300
commitf3b4e06b3bda759afd042d3d5fa86bea8f1fe278 (patch)
tree795a322f98bd67431e16e096282784f56e3d26fe
parentc8fa7a807f3c5f946bd92076fbaf7826edb650dc (diff)
downloadlinux-f3b4e06b3bda759afd042d3d5fa86bea8f1fe278.tar.xz
perf intel-pt: Fix TSC slip
A TSC packet can slip past MTC packets so that the timestamp appears to go backwards. One estimate is that can be up to about 40 CPU cycles, which is certainly less than 0x1000 TSC ticks, but accept slippage an order of magnitude more to be on the safe side. Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: stable@vger.kernel.org Fixes: 79b58424b821c ("perf tools: Add Intel PT support for decoding MTC packets") Link: http://lkml.kernel.org/r/20190325135135.18348-1-adrian.hunter@intel.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
-rw-r--r--tools/perf/util/intel-pt-decoder/intel-pt-decoder.c20
1 files changed, 8 insertions, 12 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 6e03db142091..872fab163585 100644
--- a/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
+++ b/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
@@ -251,19 +251,15 @@ struct intel_pt_decoder *intel_pt_decoder_new(struct intel_pt_params *params)
if (!(decoder->tsc_ctc_ratio_n % decoder->tsc_ctc_ratio_d))
decoder->tsc_ctc_mult = decoder->tsc_ctc_ratio_n /
decoder->tsc_ctc_ratio_d;
-
- /*
- * Allow for timestamps appearing to backwards because a TSC
- * packet has slipped past a MTC packet, so allow 2 MTC ticks
- * or ...
- */
- decoder->tsc_slip = multdiv(2 << decoder->mtc_shift,
- decoder->tsc_ctc_ratio_n,
- decoder->tsc_ctc_ratio_d);
}
- /* ... or 0x100 paranoia */
- if (decoder->tsc_slip < 0x100)
- decoder->tsc_slip = 0x100;
+
+ /*
+ * A TSC packet can slip past MTC packets so that the timestamp appears
+ * to go backwards. One estimate is that can be up to about 40 CPU
+ * cycles, which is certainly less than 0x1000 TSC ticks, but accept
+ * slippage an order of magnitude more to be on the safe side.
+ */
+ decoder->tsc_slip = 0x10000;
intel_pt_log("timestamp: mtc_shift %u\n", decoder->mtc_shift);
intel_pt_log("timestamp: tsc_ctc_ratio_n %u\n", decoder->tsc_ctc_ratio_n);