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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 <kan.liang@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
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 <acme@redhat.com>
This commit is contained in:
Kan Liang 2015-10-02 05:04:34 -04:00 committed by Arnaldo Carvalho de Melo
parent 9f065194e2
commit 19afd10410
2 changed files with 12 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
tools/perf/Documentation/perf-stat.txt
View File

@ -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

9
tools/perf/builtin-stat.c
View File

@ -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");
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))