Em Mon, Mar 25, 2019 at 03:51:35PM +0200, Adrian Hunter escreveu: > 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.
thanks, applied to perf/urgent. - Arnaldo > Signed-off-by: Adrian Hunter <[email protected]> > Fixes: 79b58424b821c ("perf tools: Add Intel PT support for decoding MTC > packets") > Cc: [email protected] > --- > .../util/intel-pt-decoder/intel-pt-decoder.c | 20 ++++++++----------- > 1 file 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); > -- > 2.17.1 -- - Arnaldo
