From: Kan Liang <[email protected]> The rough overhead rate can be caculated by the sum of all kinds of overhead / elapsed time. If the overhead rate is higher than 10%, warning the user.
Signed-off-by: Kan Liang <[email protected]> --- tools/perf/util/session.c | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c index e84808f..decfc48 100644 --- a/tools/perf/util/session.c +++ b/tools/perf/util/session.c @@ -1559,6 +1559,30 @@ perf_session__warn_order(const struct perf_session *session) ui__warning("%u out of order events recorded.\n", oe->nr_unordered_events); } +static void +perf_session__warn_overhead(const struct perf_session *session) +{ + const struct events_stats *stats = &session->evlist->stats; + double overhead_rate; + u64 overhead; + int i; + + for (i = 0; i < session->header.env.nr_cpus_online; i++) { + overhead = stats->total_nmi_overhead[i][1]; + overhead += stats->total_mux_overhead[i][1]; + overhead += stats->total_sb_overhead[i][1]; + overhead += stats->total_user_write_overhead[i][1]; + + overhead_rate = (double)overhead / (double)stats->elapsed_time; + + if (overhead_rate > 0.1) { + ui__warning("Perf overhead is high! The overhead rate is %3.2f%% on CPU %d\n\n" + "Please consider reducing the number of events, or increasing the period, or decrease the frequency.\n\n", + overhead_rate * 100.0, i); + } + } +} + static void perf_session__warn_about_errors(const struct perf_session *session) { const struct events_stats *stats = &session->evlist->stats; @@ -1632,6 +1656,8 @@ static void perf_session__warn_about_errors(const struct perf_session *session) "Increase it by --proc-map-timeout\n", stats->nr_proc_map_timeout); } + + perf_session__warn_overhead(session); } static int perf_session__flush_thread_stack(struct thread *thread, -- 2.5.5
