Messages in this thread | | | Subject | Re: [PATCH] perf stat: Improve runtime stat for interval mode | From | "Jin, Yao" <> | Date | Mon, 20 Apr 2020 13:59:41 +0800 |
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On 4/20/2020 1:48 PM, kajoljain wrote: > > > On 4/17/20 6:21 AM, Jin Yao wrote: >> For interval mode, the metric is printed after # if it exists. But >> it's not calculated by the counts generated in this interval. See >> following examples, >> >> root@kbl-ppc:~# perf stat -M CPI -I1000 --interval-count 2 >> # time counts unit events >> 1.000422803 764,809 inst_retired.any # 2.9 CPI >> 1.000422803 2,234,932 cycles >> 2.001464585 1,960,061 inst_retired.any # 1.6 CPI >> 2.001464585 4,022,591 cycles >> >> The second CPI should not be 1.6 (4,022,591/1,960,061 is 2.1) >> >> root@kbl-ppc:~# perf stat -e cycles,instructions -I1000 --interval-count 2 >> # time counts unit events >> 1.000429493 2,869,311 cycles >> 1.000429493 816,875 instructions # 0.28 insn per cycle >> 2.001516426 9,260,973 cycles >> 2.001516426 5,250,634 instructions # 0.87 insn per cycle >> >> The second 'insn per cycle' should not be 0.87 (5,250,634/9,260,973 is 0.57). >> >> The current code uses a global variable rt_stat for tracking and >> updating the std dev of runtime stat. Unlike the counts, rt_stat is >> not reset for interval. While the counts are reset for interval. >> >> perf_stat_process_counter() >> { >> if (config->interval) >> init_stats(ps->res_stats); >> } >> >> So for interval, the rt_stat should be reset either. >> >> This patch resets rt_stat before read_counters, so the runtime >> stat is only calculated by the counts generated in this interval. >> >> With this patch, >> >> root@kbl-ppc:~# perf stat -M CPI -I1000 --interval-count 2 >> # time counts unit events >> 1.000420924 2,408,818 inst_retired.any # 2.1 CPI >> 1.000420924 5,010,111 cycles >> 2.001448579 2,798,407 inst_retired.any # 1.6 CPI >> 2.001448579 4,599,861 cycles >> >> root@kbl-ppc:~# perf stat -e cycles,instructions -I1000 --interval-count 2 >> # time counts unit events >> 1.000428555 2,769,714 cycles >> 1.000428555 774,462 instructions # 0.28 insn per cycle >> 2.001471562 3,595,904 cycles >> 2.001471562 1,243,703 instructions # 0.35 insn per cycle >> > > Hi Jin, > Thanks for the patch. Was working on similar issue raised by Joakim Zhang. > Here's link to my findings: https://lkml.org/lkml/2020/3/24/158 > > This patch solves the issue. > > Acked-By: Kajol Jain <kjain@linux.ibm.com> and Tested-By: Kajol Jain <kjain@linux.ibm.com> >
Thanks for testing this patch. :)
Thanks Jin Yao
>> Now the second 'insn per cycle' and CPI are calculated by the counts >> generated in this interval. >> >> Signed-off-by: Jin Yao <yao.jin@linux.intel.com> >> --- >> tools/perf/Documentation/perf-stat.txt | 2 ++ >> tools/perf/builtin-stat.c | 1 + >> tools/perf/util/stat-shadow.c | 5 +++++ >> tools/perf/util/stat.h | 1 + >> 4 files changed, 9 insertions(+) >> >> diff --git a/tools/perf/Documentation/perf-stat.txt b/tools/perf/Documentation/perf-stat.txt >> index 4d56586b2fb9..3fb5028aef08 100644 >> --- a/tools/perf/Documentation/perf-stat.txt >> +++ b/tools/perf/Documentation/perf-stat.txt >> @@ -176,6 +176,8 @@ Print count deltas every N milliseconds (minimum: 1ms) >> 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' >> >> +If the metric exists, it is calculated by the counts generated in this interval and the metric is printed after #. >> + >> --interval-count times:: >> Print count deltas for fixed number of times. >> This option should be used together with "-I" option. >> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c >> index ec053dc1e35c..d5c326ff46d0 100644 >> --- a/tools/perf/builtin-stat.c >> +++ b/tools/perf/builtin-stat.c >> @@ -359,6 +359,7 @@ static void process_interval(void) >> clock_gettime(CLOCK_MONOTONIC, &ts); >> diff_timespec(&rs, &ts, &ref_time); >> >> + perf_stat__reset_rt_stat(); >> read_counters(&rs); >> >> if (STAT_RECORD) { >> diff --git a/tools/perf/util/stat-shadow.c b/tools/perf/util/stat-shadow.c >> index 1ad5c5be7e97..c8f5ca6c8749 100644 >> --- a/tools/perf/util/stat-shadow.c >> +++ b/tools/perf/util/stat-shadow.c >> @@ -186,6 +186,11 @@ void perf_stat__reset_shadow_stats(void) >> memset(&walltime_nsecs_stats, 0, sizeof(walltime_nsecs_stats)); >> } >> >> +void perf_stat__reset_rt_stat(void) >> +{ >> + reset_stat(&rt_stat); >> +} >> + >> void perf_stat__reset_shadow_per_stat(struct runtime_stat *st) >> { >> reset_stat(st); >> diff --git a/tools/perf/util/stat.h b/tools/perf/util/stat.h >> index b4fdfaa7f2c0..2975494166dd 100644 >> --- a/tools/perf/util/stat.h >> +++ b/tools/perf/util/stat.h >> @@ -176,6 +176,7 @@ void runtime_stat__init(struct runtime_stat *st); >> void runtime_stat__exit(struct runtime_stat *st); >> void perf_stat__init_shadow_stats(void); >> void perf_stat__reset_shadow_stats(void); >> +void perf_stat__reset_rt_stat(void); >> void perf_stat__reset_shadow_per_stat(struct runtime_stat *st); >> void perf_stat__update_shadow_stats(struct evsel *counter, u64 count, >> int cpu, struct runtime_stat *st); >>
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