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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 <eranian@google.com> Reviewed-by: Ian Rogers <irogers@google.com> Acked-by: Jiri Olsa <jolsa@redhat.com> Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Alexey Budankov <alexey.budankov@linux.intel.com> Cc: Kan Liang <kan.liang@linux.intel.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Tony Jones <tonyj@suse.de> Cc: yuzhoujian <yuzhoujian@didichuxing.com> Link: http://lore.kernel.org/lkml/20200422155038.9380-1-irogers@google.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> |
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| .. | ||
| android.txt | ||
| asciidoc.conf | ||
| asciidoctor-extensions.rb | ||
| build-xed.txt | ||
| Build.txt | ||
| callchain-overhead-calculation.txt | ||
| db-export.txt | ||
| examples.txt | ||
| intel-bts.txt | ||
| intel-pt.txt | ||
| itrace.txt | ||
| jit-interface.txt | ||
| jitdump-specification.txt | ||
| Makefile | ||
| manpage-1.72.xsl | ||
| manpage-base.xsl | ||
| manpage-bold-literal.xsl | ||
| manpage-normal.xsl | ||
| manpage-suppress-sp.xsl | ||
| perf-annotate.txt | ||
| perf-archive.txt | ||
| perf-bench.txt | ||
| perf-buildid-cache.txt | ||
| perf-buildid-list.txt | ||
| perf-c2c.txt | ||
| perf-config.txt | ||
| perf-data.txt | ||
| perf-diff.txt | ||
| perf-evlist.txt | ||
| perf-ftrace.txt | ||
| perf-help.txt | ||
| perf-inject.txt | ||
| perf-intel-pt.txt | ||
| perf-kallsyms.txt | ||
| perf-kmem.txt | ||
| perf-kvm.txt | ||
| perf-list.txt | ||
| perf-lock.txt | ||
| perf-mem.txt | ||
| perf-probe.txt | ||
| perf-record.txt | ||
| perf-report.txt | ||
| perf-sched.txt | ||
| perf-script-perl.txt | ||
| perf-script-python.txt | ||
| perf-script.txt | ||
| perf-stat.txt | ||
| perf-test.txt | ||
| perf-timechart.txt | ||
| perf-top.txt | ||
| perf-trace.txt | ||
| perf-version.txt | ||
| perf.data-directory-format.txt | ||
| perf.data-file-format.txt | ||
| perf.txt | ||
| perfconfig.example | ||
| tips.txt | ||