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Date: Mon, 20 Apr 2020 13:59:41 +0800
From: "Jin, Yao" <yao.jin@...ux.intel.com>
To: kajoljain <kjain@...ux.ibm.com>, acme@...nel.org, jolsa@...nel.org,
peterz@...radead.org, mingo@...hat.com,
alexander.shishkin@...ux.intel.com
Cc: Linux-kernel@...r.kernel.org, ak@...ux.intel.com,
kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH] perf stat: Improve runtime stat for interval mode
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@...-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@...-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@...-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@...-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@...ux.ibm.com> and Tested-By: Kajol Jain <kjain@...ux.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@...ux.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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