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Date: Tue, 21 Apr 2020 22:08:43 -0300
From: Arnaldo Melo <arnaldo.melo@...il.com>
To: "Jin, Yao" <yao.jin@...ux.intel.com>
CC: jolsa@...nel.org, peterz@...radead.org, mingo@...hat.com,
alexander.shishkin@...ux.intel.com, Linux-kernel@...r.kernel.org,
ak@...ux.intel.com, kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH v2] perf stat: Improve runtime stat for interval mode
On April 21, 2020 9:53:41 PM GMT-03:00, "Jin, Yao" <yao.jin@...ux.intel.com> wrote:
>Hi Arnaldo,
>
>On 4/21/2020 9:53 PM, Arnaldo Carvalho de Melo wrote:
>> Em Mon, Apr 20, 2020 at 10:54:17PM +0800, Jin Yao escreveu:
>>> 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.
>>
>> s/either/too/g right?
>>
>
>Yes, should use "too" here. :)
Ok
>
>> And please try and find what was the cset that introduced the
>problem,
>> so that we can have a Fixes: line and the stable series can pick it,
>ok?
> >
>> - Arnaldo
>>
>
>I have tried to find the patch which introduced this issue.
>
>51fd2df1e882 ("perf stat: Fix interval output values").
>
>This patch zeros stats for interval mode. I just think it should reset
>rt_stat too.
>
>But I really don't know if it's fair to this patch so I don't add it in
>
>my patch description.
That's ok, this just speeds up the process, I'll check it :-)
- Arnaldo
>
>Thanks
>Jin Yao
>
>>> 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
>>>
>>> Now the second 'insn per cycle' and CPI are calculated by the counts
>>> generated in this interval.
>>>
>>> v2:
>>> ---
>>> Use just existing perf_stat__reset_shadow_per_stat(&rt_stat).
>>> We don't need to define new function perf_stat__reset_rt_stat.
>>>
>>> Signed-off-by: Jin Yao <yao.jin@...ux.intel.com>
>>> ---
>>> tools/perf/Documentation/perf-stat.txt | 2 ++
>>> tools/perf/builtin-stat.c | 1 +
>>> 2 files changed, 3 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 9207b6c45475..3f050d85c277 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_shadow_per_stat(&rt_stat);
>>> read_counters(&rs);
>>>
>>> if (STAT_RECORD) {
>>> --
>>> 2.17.1
>>>
>>
--
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