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perf annotate: Add comment about annotated_src->nr_histograms

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When we have multiple groups in an evlist, say:

  $ perf stat -e '{cycles,instructions},{cache-references,cache-misses}' sleep 1

   Performance counter stats for 'sleep 1':

           343,134      cycles:u
           249,292      instructions:u            #    0.73  insn per cycle
            15,556      cache-references:u
             8,925      cache-misses:u            #   57.373 % of all cache refs

       1.000957550 seconds time elapsed

  $

Then the perf_evsel instances for the two group leaders ("cycles" and
"cache-references") will have evsel->nr_members set to 2, while all the
evsel->evlist->nr_entries will be set to 4, so we can't use
evsel->evlist->nr_entries everywhere, as event groups need to be taken
into account.

But this probably requires us to audit at least the forced-group code,
where we want all of the events to be in a "group", to see them all in
the screen, one column for each, even knowing that they were not
necessarily scheduled to count at the same time by the kernel perf
subsystem.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-2g0vwqnc49wl4ttjk8dvpgcc@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Arnaldo Carvalho de Melo 2018-05-25 11:27:38 -03:00
parent 9fd5578a3c
commit 9132d3d92d
1 changed files with 4 additions and 0 deletions
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4
tools/perf/util/annotate.h
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@ -202,6 +202,10 @@ struct cyc_hist {
/** struct annotated_source - symbols with hits have this attached as in sannotation
*
* @histograms: Array of addr hit histograms per event being monitored
* nr_histograms: This may not be the same as evsel->evlist->nr_entries if
* we have more than a group in a evlist, where we will want
* to see each group separately, that is why symbol__annotate2()
* sets src->nr_histograms to evsel->nr_members.
* @lines: If 'print_lines' is specified, per source code line percentages
* @source: source parsed from a disassembler like objdump -dS
* @cyc_hist: Average cycles per basic block