From 19afd10410957b1c808c2c49a88e6dd8b23aa894 Mon Sep 17 00:00:00 2001 From: Kan Liang Date: Fri, 2 Oct 2015 05:04:34 -0400 Subject: [PATCH] perf stat: Reduce min --interval-print to 10ms The --interval-print parameter was limited to 100ms. However, for example, 10ms is required to do sophisticated bandwidth analysis using uncore events. The test shows that the overhead of the system-wide uncore monitoring with 10ms interval is only ~2%. So this patch reduces the minimal interval-print allowd to 10ms. But 10ms may not work well for all cases. For example, when the cpus/threads number is very large, for system-wide core event monitoring the overhead could be high. To handle this issue, a warning will be displayed when the interval-print is set between 10ms to 100ms. So users can make a decision according to their specific cases. # perf stat -e uncore_imc_1/cas_count_read/ -a --interval-print 10 -- sleep 1 print interval < 100ms. The overhead percentage could be high in some cases. Please proceed with caution. # time counts unit events 0.010200451 0.10 MiB uncore_imc_1/cas_count_read/ 0.020475117 0.02 MiB uncore_imc_1/cas_count_read/ 0.030692800 0.01 MiB uncore_imc_1/cas_count_read/ 0.040948161 0.02 MiB uncore_imc_1/cas_count_read/ 0.051159564 0.00 MiB uncore_imc_1/cas_count_read/ Signed-off-by: Kan Liang Acked-by: Jiri Olsa Cc: Andi Kleen Cc: Namhyung Kim Link: http://lkml.kernel.org/r/1443776674-42511-1-git-send-email-kan.liang@intel.com [ Added warning about overhead when using sub 100ms intervals to the man page ] Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/Documentation/perf-stat.txt | 5 +++-- tools/perf/builtin-stat.c | 13 +++++++++---- 2 files changed, 12 insertions(+), 6 deletions(-) diff --git a/tools/perf/Documentation/perf-stat.txt b/tools/perf/Documentation/perf-stat.txt index 47469abdcc1c..4e074a660826 100644 --- a/tools/perf/Documentation/perf-stat.txt +++ b/tools/perf/Documentation/perf-stat.txt @@ -128,8 +128,9 @@ perf stat --repeat 10 --null --sync --pre 'make -s O=defconfig-build/clean' -- m -I msecs:: --interval-print msecs:: - Print count deltas every N milliseconds (minimum: 100ms) - example: perf stat -I 1000 -e cycles -a sleep 5 +Print count deltas every N milliseconds (minimum: 10ms) +The overhead percentage could be high in some cases, for instance with small, sub 100ms intervals. Use with caution. + example: 'perf stat -I 1000 -e cycles -a sleep 5' --per-socket:: Aggregate counts per processor socket for system-wide mode measurements. This diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c index a96fb5c3bedb..5ef88f760b12 100644 --- a/tools/perf/builtin-stat.c +++ b/tools/perf/builtin-stat.c @@ -1179,7 +1179,7 @@ int cmd_stat(int argc, const char **argv, const char *prefix __maybe_unused) OPT_STRING(0, "post", &post_cmd, "command", "command to run after to the measured command"), OPT_UINTEGER('I', "interval-print", &stat_config.interval, - "print counts at regular interval in ms (>= 100)"), + "print counts at regular interval in ms (>= 10)"), OPT_SET_UINT(0, "per-socket", &stat_config.aggr_mode, "aggregate counts per processor socket", AGGR_SOCKET), OPT_SET_UINT(0, "per-core", &stat_config.aggr_mode, @@ -1332,9 +1332,14 @@ int cmd_stat(int argc, const char **argv, const char *prefix __maybe_unused) thread_map__read_comms(evsel_list->threads); if (interval && interval < 100) { - pr_err("print interval must be >= 100ms\n"); - parse_options_usage(stat_usage, options, "I", 1); - goto out; + if (interval < 10) { + pr_err("print interval must be >= 10ms\n"); + parse_options_usage(stat_usage, options, "I", 1); + goto out; + } else + pr_warning("print interval < 100ms. " + "The overhead percentage could be high in some cases. " + "Please proceed with caution.\n"); } if (perf_evlist__alloc_stats(evsel_list, interval))