From 411916880ff4061ac0491a154f10af4d49a0c61a Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Fri, 2 Aug 2013 17:41:11 -0700 Subject: [PATCH] perf stat: Add support for --initial-delay option When measuring workloads the startup phase -- doing page faults, dynamic linking, opening files -- is often very different from the rest of the workload. Especially with smaller kernels and using counter multiplexing this can give significant measurement errors. Multiplexing assumes that the workload is mostly the same over longer periods. But at startup there is typically some spike of activity which is relatively short. If many groups are multiplexing the one group seeing the spike, and which is then scaled up over the time to run all groups, may see a significant error. Also in general it's often not useful to measure the startup, because it is so different from the rest. One way around this is to use interval mode and discard the first sample, but this can be awkward because interval mode doesn't support intervals of less than 100ms, and also a useful interval is not necessarily the same as a useful startup delay. This patch adds a new --initial-delay / -D option to skip measuring for the startup phase. The time can be specified in ms Here's a simple example: perf stat -e page-faults bash -c 'for i in $(seq 100000) ; do true ; done' ... 3,721 page-faults ... If we just wait 20 ms the number of page faults is 1/3 less: perf stat -D 20 -e page-faults bash -c 'for i in $(seq 100000) ; do true ; done' ... 2,823 page-faults ... So we filtered out most of the startup noise from bash. Signed-off-by: Andi Kleen Reviewed-by: Jiri Olsa Cc: Jiri Olsa Cc: Stephane Eranian Link: http://lkml.kernel.org/r/1375490473-1503-4-git-send-email-andi@firstfloor.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/Documentation/perf-stat.txt | 5 +++++ tools/perf/builtin-stat.c | 22 +++++++++++++++++++++- 2 files changed, 26 insertions(+), 1 deletion(-) diff --git a/tools/perf/Documentation/perf-stat.txt b/tools/perf/Documentation/perf-stat.txt index 2fe87fb558f0..73c9759005a3 100644 --- a/tools/perf/Documentation/perf-stat.txt +++ b/tools/perf/Documentation/perf-stat.txt @@ -132,6 +132,11 @@ is a useful mode to detect imbalance between physical cores. To enable this mod use --per-core in addition to -a. (system-wide). The output includes the core number and the number of online logical processors on that physical processor. +-D msecs:: +--initial-delay msecs:: +After starting the program, wait msecs before measuring. This is useful to +filter out the startup phase of the program, which is often very different. + EXAMPLES -------- diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c index 352fbd7ff4a1..2e637e4c951d 100644 --- a/tools/perf/builtin-stat.c +++ b/tools/perf/builtin-stat.c @@ -100,6 +100,7 @@ static const char *pre_cmd = NULL; static const char *post_cmd = NULL; static bool sync_run = false; static unsigned int interval = 0; +static unsigned int initial_delay = 0; static bool forever = false; static struct timespec ref_time; static struct cpu_map *aggr_map; @@ -254,7 +255,8 @@ static int create_perf_stat_counter(struct perf_evsel *evsel) if (!perf_target__has_task(&target) && perf_evsel__is_group_leader(evsel)) { attr->disabled = 1; - attr->enable_on_exec = 1; + if (!initial_delay) + attr->enable_on_exec = 1; } return perf_evsel__open_per_thread(evsel, evsel_list->threads); @@ -416,6 +418,20 @@ static void print_interval(void) } } +static void handle_initial_delay(void) +{ + struct perf_evsel *counter; + + if (initial_delay) { + const int ncpus = cpu_map__nr(evsel_list->cpus), + nthreads = thread_map__nr(evsel_list->threads); + + usleep(initial_delay * 1000); + list_for_each_entry(counter, &evsel_list->entries, node) + perf_evsel__enable(counter, ncpus, nthreads); + } +} + static int __run_perf_stat(int argc, const char **argv) { char msg[512]; @@ -486,6 +502,7 @@ static int __run_perf_stat(int argc, const char **argv) if (forks) { perf_evlist__start_workload(evsel_list); + handle_initial_delay(); if (interval) { while (!waitpid(child_pid, &status, WNOHANG)) { @@ -497,6 +514,7 @@ static int __run_perf_stat(int argc, const char **argv) if (WIFSIGNALED(status)) psignal(WTERMSIG(status), argv[0]); } else { + handle_initial_delay(); while (!done) { nanosleep(&ts, NULL); if (interval) @@ -1419,6 +1437,8 @@ int cmd_stat(int argc, const char **argv, const char *prefix __maybe_unused) "aggregate counts per processor socket", AGGR_SOCKET), OPT_SET_UINT(0, "per-core", &aggr_mode, "aggregate counts per physical processor core", AGGR_CORE), + OPT_UINTEGER('D', "delay", &initial_delay, + "ms to wait before starting measurement after program start"), OPT_END() }; const char * const stat_usage[] = { -- 2.39.5