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perf intel-pt: Document IPC usage

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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>
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Adrian Hunter 2019-05-20 14:37:18 +03:00 committed by Arnaldo Carvalho de Melo
parent 3f05516758
commit 5db47f43cc
1 changed files with 30 additions and 0 deletions
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tools/perf/Documentation/intel-pt.txt
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@ -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,