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| author | Kan Liang <kan.liang@intel.com> | 2015-10-02 11:04:34 +0200 |
|---|---|---|
| committer | Arnaldo Carvalho de Melo <acme@redhat.com> | 2015-10-02 22:07:55 +0200 |
| commit | 19afd10410957b1c808c2c49a88e6dd8b23aa894 (patch) | |
| tree | 7c00b3eb48b51e28c3d80b56bdd9c2e6066a4b1b /tools/perf/Documentation | |
| parent | perf record: Change 'record.samples' type to unsigned long long (diff) | |
| download | linux-19afd10410957b1c808c2c49a88e6dd8b23aa894.tar.xz linux-19afd10410957b1c808c2c49a88e6dd8b23aa894.zip | |
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>
Diffstat (limited to 'tools/perf/Documentation')
| -rw-r--r-- | tools/perf/Documentation/perf-stat.txt | 5 |
1 files changed, 3 insertions, 2 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 |