linux-kernel - Re: [PATCH v4 3/4] perf stat: Copy counts from prev_raw

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Date:   Thu, 14 May 2020 13:42:39 +0800
From:   "Jin, Yao" <yao.jin@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     acme@...nel.org, 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 v4 3/4] perf stat: Copy counts from prev_raw_counts to
 evsel->counts

Hi Jiri,

On 5/13/2020 11:31 PM, Jiri Olsa wrote:
> On Fri, May 08, 2020 at 03:58:16PM +0800, Jin Yao wrote:
>> It would be useful to support the overall statistics for perf-stat
>> interval mode. For example, report the summary at the end of
>> "perf-stat -I" output.
>>
>> But since perf-stat can support many aggregation modes, such as
>> --per-thread, --per-socket, -M and etc, we need a solution which
>> doesn't bring much complexity.
>>
>> The idea is to use 'evsel->prev_raw_counts' which is updated in
>> each interval and it's saved with the latest counts. Before reporting
>> the summary, we copy the counts from evsel->prev_raw_counts to
>> evsel->counts, and next we just follow non-interval processing.
>>
>> In evsel__compute_deltas, this patch saves counts to the member
>> [cpu0,thread0] of perf_counts for AGGR_GLOBAL.
>>
>> That's because after copying evsel->prev_raw_counts to evsel->counts,
>> perf_counts(evsel->counts, cpu, thread) are all 0 for AGGR_GLOBAL.
>> Once we go to process_counter_maps again, all members of perf_counts
>> are 0.
>>
>> So this patch uses a trick that saves the previous aggr value to
>> the member [cpu0,thread0] of perf_counts, then aggr calculation
>> in process_counter_values can work correctly.
>>
>>   v4:
>>   ---
>>   Change the commit message.
>>   No functional change.
>>
>> Signed-off-by: Jin Yao <yao.jin@...ux.intel.com>
>> ---
>>   tools/perf/util/evsel.c |  1 +
>>   tools/perf/util/stat.c  | 24 ++++++++++++++++++++++++
>>   tools/perf/util/stat.h  |  1 +
>>   3 files changed, 26 insertions(+)
>>
>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
>> index 28683b0eb738..6fae1ec28886 100644
>> --- a/tools/perf/util/evsel.c
>> +++ b/tools/perf/util/evsel.c
>> @@ -1283,6 +1283,7 @@ void evsel__compute_deltas(struct evsel *evsel, int cpu, int thread,
>>   	if (cpu == -1) {
>>   		tmp = evsel->prev_raw_counts->aggr;
>>   		evsel->prev_raw_counts->aggr = *count;
>> +		*perf_counts(evsel->prev_raw_counts, 0, 0) = *count;
> 
> ok, I think I understand that now.. it's only for AGGR_GLOBAL mode,
> because the perf_stat_process_counter will create aggr values from
> per cpu values
> 
> but why do we need to do that all the time? can't we just set it up
> before you zero prev_raw_counts in next patch?
> 
> 
>          if (interval) {
>                  stat_config.interval = 0;
>                  stat_config.summary = true;
>                  perf_evlist__copy_prev_raw_counts(evsel_list);
> 
> 	-> for AGGR_GLOBAL set the counts[0,0] to prev_raw_counts->aggr
> 
>                  perf_evlist__reset_prev_raw_counts(evsel_list);
>                  runtime_stat_reset(&stat_config);
>                  perf_stat__reset_shadow_per_stat(&rt_stat);
>          }
>


Yes, I think that's a good idea.

Now in v5, I create a new patch "perf stat: Save aggr value to first member of 
prev_raw_counts" to save aggr value to first member of prev_raw_counts for 
AGGR_GLOBAL. Then next, perf_stat_process_counter can create aggr values from 
per cpu values successfully.

Thanks
Jin Yao

> 
> thanks,
> jirka
>