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

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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>
This commit is contained in:
Adrian Hunter 2017-05-26 11:17:37 +03:00 committed by Arnaldo Carvalho de Melo
parent ead2bfdb85
commit 38b65b0891
1 changed files with 14 additions and 0 deletions
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14
tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
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@ -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);
}