From d99c22eabee45f40ca44b877a1adde028f14b6b4 Mon Sep 17 00:00:00 2001 From: Stephane Eranian Date: Wed, 22 Apr 2020 08:50:38 -0700 Subject: [PATCH] perf record: Add num-synthesize-threads option To control degree of parallelism of the synthesize_mmap() code which is scanning /proc/PID/task/PID/maps and can be time consuming. Mimic perf top way of handling the option. If not specified will default to 1 thread, i.e. default behavior before this option. On a desktop computer the processing of /proc/PID/task/PID/maps isn't slow enough to warrant parallel processing and the thread creation has some cost - hence the default of 1. On a loaded server with >100 cores it is possible to see synthesis times in the order of seconds and in this case having the option is desirable. As the processing is a synchronization point, it is legitimate to worry if Amdahl's law will apply to this patch. Profiling with this patch in place: https://lore.kernel.org/lkml/20200415054050.31645-4-irogers@google.com/ shows: ... - 32.59% __perf_event__synthesize_threads - 32.54% __event__synthesize_thread + 22.13% perf_event__synthesize_mmap_events + 6.68% perf_event__get_comm_ids.constprop.0 + 1.49% process_synthesized_event + 1.29% __GI___readdir64 + 0.60% __opendir ... That is the processing is 1.49% of execution time and there is plenty to make parallel. This is shown in the benchmark in this patch: https://lore.kernel.org/lkml/20200415054050.31645-2-irogers@google.com/ Computing performance of multi threaded perf event synthesis by synthesizing events on CPU 0: Number of synthesis threads: 1 Average synthesis took: 127729.000 usec (+- 3372.880 usec) Average num. events: 21548.600 (+- 0.306) Average time per event 5.927 usec Number of synthesis threads: 2 Average synthesis took: 88863.500 usec (+- 385.168 usec) Average num. events: 21552.800 (+- 0.327) Average time per event 4.123 usec Number of synthesis threads: 3 Average synthesis took: 83257.400 usec (+- 348.617 usec) Average num. events: 21553.200 (+- 0.327) Average time per event 3.863 usec Number of synthesis threads: 4 Average synthesis took: 75093.000 usec (+- 422.978 usec) Average num. events: 21554.200 (+- 0.200) Average time per event 3.484 usec Number of synthesis threads: 5 Average synthesis took: 64896.600 usec (+- 353.348 usec) Average num. events: 21558.000 (+- 0.000) Average time per event 3.010 usec Number of synthesis threads: 6 Average synthesis took: 59210.200 usec (+- 342.890 usec) Average num. events: 21560.000 (+- 0.000) Average time per event 2.746 usec Number of synthesis threads: 7 Average synthesis took: 54093.900 usec (+- 306.247 usec) Average num. events: 21562.000 (+- 0.000) Average time per event 2.509 usec Number of synthesis threads: 8 Average synthesis took: 48938.700 usec (+- 341.732 usec) Average num. events: 21564.000 (+- 0.000) Average time per event 2.269 usec Where average time per synthesized event goes from 5.927 usec with 1 thread to 2.269 usec with 8. This isn't a linear speed up as not all of synthesize code has been made parallel. If the synthesis time was about 10 seconds then using 8 threads may bring this down to less than 4. Signed-off-by: Stephane Eranian Reviewed-by: Ian Rogers Acked-by: Jiri Olsa Cc: Adrian Hunter Cc: Alexander Shishkin Cc: Alexey Budankov Cc: Kan Liang Cc: Mark Rutland Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Tony Jones Cc: yuzhoujian Link: http://lore.kernel.org/lkml/20200422155038.9380-1-irogers@google.com Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/Documentation/perf-record.txt | 4 +++ tools/perf/builtin-record.c | 34 ++++++++++++++++++++++-- tools/perf/util/record.h | 1 + 3 files changed, 37 insertions(+), 2 deletions(-) diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt index b3f3b3f1c161..6e8b4649307c 100644 --- a/tools/perf/Documentation/perf-record.txt +++ b/tools/perf/Documentation/perf-record.txt @@ -596,6 +596,10 @@ Make a copy of /proc/kcore and place it into a directory with the perf data file Limit the sample data max size, is expected to be a number with appended unit character - B/K/M/G +--num-thread-synthesize:: + The number of threads to run when synthesizing events for existing processes. + By default, the number of threads equals 1. + SEE ALSO -------- linkperf:perf-stat[1], linkperf:perf-list[1], linkperf:perf-intel-pt[1] diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c index 1ab349abe904..2e8011f179f2 100644 --- a/tools/perf/builtin-record.c +++ b/tools/perf/builtin-record.c @@ -43,6 +43,7 @@ #include "util/time-utils.h" #include "util/units.h" #include "util/bpf-event.h" +#include "util/util.h" #include "asm/bug.h" #include "perf.h" @@ -50,6 +51,7 @@ #include #include #include +#include #include #include #include @@ -503,6 +505,20 @@ static int process_synthesized_event(struct perf_tool *tool, return record__write(rec, NULL, event, event->header.size); } +static int process_locked_synthesized_event(struct perf_tool *tool, + union perf_event *event, + struct perf_sample *sample __maybe_unused, + struct machine *machine __maybe_unused) +{ + static pthread_mutex_t synth_lock = PTHREAD_MUTEX_INITIALIZER; + int ret; + + pthread_mutex_lock(&synth_lock); + ret = process_synthesized_event(tool, event, sample, machine); + pthread_mutex_unlock(&synth_lock); + return ret; +} + static int record__pushfn(struct mmap *map, void *to, void *bf, size_t size) { struct record *rec = to; @@ -1288,6 +1304,7 @@ static int record__synthesize(struct record *rec, bool tail) struct perf_tool *tool = &rec->tool; int fd = perf_data__fd(data); int err = 0; + event_op f = process_synthesized_event; if (rec->opts.tail_synthesize != tail) return 0; @@ -1402,9 +1419,18 @@ static int record__synthesize(struct record *rec, bool tail) if (err < 0) pr_warning("Couldn't synthesize cgroup events.\n"); + if (rec->opts.nr_threads_synthesize > 1) { + perf_set_multithreaded(); + f = process_locked_synthesized_event; + } + err = __machine__synthesize_threads(machine, tool, &opts->target, rec->evlist->core.threads, - process_synthesized_event, opts->sample_address, - 1); + f, opts->sample_address, + rec->opts.nr_threads_synthesize); + + if (rec->opts.nr_threads_synthesize > 1) + perf_set_singlethreaded(); + out: return err; } @@ -2232,6 +2258,7 @@ static struct record record = { .default_per_cpu = true, }, .mmap_flush = MMAP_FLUSH_DEFAULT, + .nr_threads_synthesize = 1, }, .tool = { .sample = process_sample_event, @@ -2421,6 +2448,9 @@ static struct option __record_options[] = { #endif OPT_CALLBACK(0, "max-size", &record.output_max_size, "size", "Limit the maximum size of the output file", parse_output_max_size), + OPT_UINTEGER(0, "num-thread-synthesize", + &record.opts.nr_threads_synthesize, + "number of threads to run for event synthesis"), OPT_END() }; diff --git a/tools/perf/util/record.h b/tools/perf/util/record.h index 24316458be20..923565c3b155 100644 --- a/tools/perf/util/record.h +++ b/tools/perf/util/record.h @@ -68,6 +68,7 @@ struct record_opts { int affinity; int mmap_flush; unsigned int comp_level; + unsigned int nr_threads_synthesize; }; extern const char * const *record_usage;