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    Subject[PATCH 07/27] perf report: Cache cumulative callchains
    Date
    It is possble that a callchain has cycles or recursive calls.  In that
    case it'll end up having entries more than 100% overhead in the
    output. In order to prevent such entries, cache each callchain node
    and skip if same entry already cumulated.

    Tested-by: Arun Sharma <asharma@fb.com>
    Tested-by: Rodrigo Campos <rodrigo@sdfg.com.ar>
    Acked-by: Jiri Olsa <jolsa@redhat.com>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Signed-off-by: Namhyung Kim <namhyung@kernel.org>
    ---
    tools/perf/util/hist.c | 42 ++++++++++++++++++++++++++++++++++++++++++
    1 file changed, 42 insertions(+)

    diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
    index 37c28fc13dc3..bf03db528db6 100644
    --- a/tools/perf/util/hist.c
    +++ b/tools/perf/util/hist.c
    @@ -700,7 +700,22 @@ static int
    iter_prepare_cumulative_entry(struct hist_entry_iter *iter __maybe_unused,
    struct addr_location *al __maybe_unused)
    {
    + struct hist_entry **he_cache;
    +
    callchain_cursor_commit(&callchain_cursor);
    +
    + /*
    + * This is for detecting cycles or recursions so that they're
    + * cumulated only one time to prevent entries more than 100%
    + * overhead.
    + */
    + he_cache = malloc(sizeof(*he_cache) * (PERF_MAX_STACK_DEPTH + 1));
    + if (he_cache == NULL)
    + return -ENOMEM;
    +
    + iter->priv = he_cache;
    + iter->curr = 0;
    +
    return 0;
    }

    @@ -710,6 +725,7 @@ iter_add_single_cumulative_entry(struct hist_entry_iter *iter,
    {
    struct perf_evsel *evsel = iter->evsel;
    struct perf_sample *sample = iter->sample;
    + struct hist_entry **he_cache = iter->priv;
    struct hist_entry *he;
    int err = 0;

    @@ -720,6 +736,7 @@ iter_add_single_cumulative_entry(struct hist_entry_iter *iter,
    return -ENOMEM;

    iter->he = he;
    + he_cache[iter->curr++] = he;

    /*
    * The iter->he will be over-written after ->add_next_entry()
    @@ -754,7 +771,29 @@ iter_add_next_cumulative_entry(struct hist_entry_iter *iter,
    {
    struct perf_evsel *evsel = iter->evsel;
    struct perf_sample *sample = iter->sample;
    + struct hist_entry **he_cache = iter->priv;
    struct hist_entry *he;
    + struct hist_entry he_tmp = {
    + .cpu = al->cpu,
    + .thread = al->thread,
    + .comm = thread__comm(al->thread),
    + .ip = al->addr,
    + .ms = {
    + .map = al->map,
    + .sym = al->sym,
    + },
    + .parent = iter->parent,
    + };
    + int i;
    +
    + /*
    + * Check if there's duplicate entries in the callchain.
    + * It's possible that it has cycles or recursive calls.
    + */
    + for (i = 0; i < iter->curr; i++) {
    + if (hist_entry__cmp(he_cache[i], &he_tmp) == 0)
    + return 0;
    + }

    he = __hists__add_entry(&evsel->hists, al, iter->parent, NULL, NULL,
    sample->period, sample->weight,
    @@ -763,6 +802,7 @@ iter_add_next_cumulative_entry(struct hist_entry_iter *iter,
    return -ENOMEM;

    iter->he = he;
    + he_cache[iter->curr++] = he;

    return 0;
    }
    @@ -771,7 +811,9 @@ static int
    iter_finish_cumulative_entry(struct hist_entry_iter *iter,
    struct addr_location *al __maybe_unused)
    {
    + zfree(&iter->priv);
    iter->he = NULL;
    +
    return 0;
    }

    --
    1.9.2


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