perf intel-pt: Fix TSC slip

[android-x86/kernel.git] / tools / perf / util / intel-pt-decoder / intel-pt-decoder.c

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 94764ef..3c13726 100644 (file)
--- a/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
+++ b/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
@@ -240,19 +240,15 @@ 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);