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    Subject[PATCH 15/85] perf intel-pt: Document IPC usage
    Date
    From: Adrian Hunter <adrian.hunter@intel.com>

    Add brief documentation about instructions-per-cycle (IPC) information
    derived from Intel PT.

    Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Link: http://lkml.kernel.org/r/20190520113728.14389-13-adrian.hunter@intel.com
    Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
    ---
    tools/perf/Documentation/intel-pt.txt | 30 +++++++++++++++++++++++++++
    1 file changed, 30 insertions(+)

    diff --git a/tools/perf/Documentation/intel-pt.txt b/tools/perf/Documentation/intel-pt.txt
    index 60d99e5e7921..50c5b60101bd 100644
    --- a/tools/perf/Documentation/intel-pt.txt
    +++ b/tools/perf/Documentation/intel-pt.txt
    @@ -103,6 +103,36 @@ The flags are "bcrosyiABEx" which stand for branch, call, return, conditional,
    system, asynchronous, interrupt, transaction abort, trace begin, trace end, and
    in transaction, respectively.

    +Another interesting field that is not printed by default is 'ipc' which can be
    +displayed as follows:
    +
    + perf script --itrace=be -F+ipc
    +
    +There are two ways that instructions-per-cycle (IPC) can be calculated depending
    +on the recording.
    +
    +If the 'cyc' config term (see config terms section below) was used, then IPC is
    +calculated using the cycle count from CYC packets, otherwise MTC packets are
    +used - refer to the 'mtc' config term. When MTC is used, however, the values
    +are less accurate because the timing is less accurate.
    +
    +Because Intel PT does not update the cycle count on every branch or instruction,
    +the values will often be zero. When there are values, they will be the number
    +of instructions and number of cycles since the last update, and thus represent
    +the average IPC since the last IPC for that event type. Note IPC for "branches"
    +events is calculated separately from IPC for "instructions" events.
    +
    +Also note that the IPC instruction count may or may not include the current
    +instruction. If the cycle count is associated with an asynchronous branch
    +(e.g. page fault or interrupt), then the instruction count does not include the
    +current instruction, otherwise it does. That is consistent with whether or not
    +that instruction has retired when the cycle count is updated.
    +
    +Another note, in the case of "branches" events, non-taken branches are not
    +presently sampled, so IPC values for them do not appear e.g. a CYC packet with a
    +TNT packet that starts with a non-taken branch. To see every possible IPC
    +value, "instructions" events can be used e.g. --itrace=i0ns
    +
    While it is possible to create scripts to analyze the data, an alternative
    approach is available to export the data to a sqlite or postgresql database.
    Refer to script export-to-sqlite.py or export-to-postgresql.py for more details,
    --
    2.20.1
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