Re: [PATCH v1 15/15] perf, tools: Support duration_time

[Jiri Olsa <jolsa@redhat.com>]

On Mon, Jul 24, 2017 at 04:40:15PM -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@linux.intel.com>
> 
> Some of the metrics formulas (like GFLOPs) need to know how long
> the measurement period is. Support an internal event called duration_time, which
> reports time in second. It maps to the dummy event, but is
> special cased for statistics to report the walltime duration.
> 
> So far it is not printed, but only used internally for metrics.
> 
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
> ---
>  tools/perf/util/parse-events.l |  1 +
>  tools/perf/util/stat-shadow.c  | 17 +++++++++++++----
>  2 files changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/util/parse-events.l b/tools/perf/util/parse-events.l
> index 07ee5bb3a8b0..f7bc74f8a615 100644
> --- a/tools/perf/util/parse-events.l
> +++ b/tools/perf/util/parse-events.l
> @@ -277,6 +277,7 @@ cpu-migrations|migrations			{ return sym(yyscanner, PERF_TYPE_SOFTWARE, PERF_COU
>  alignment-faults				{ return sym(yyscanner, PERF_TYPE_SOFTWARE, PERF_COUNT_SW_ALIGNMENT_FAULTS); }
>  emulation-faults				{ return sym(yyscanner, PERF_TYPE_SOFTWARE, PERF_COUNT_SW_EMULATION_FAULTS); }
>  dummy						{ return sym(yyscanner, PERF_TYPE_SOFTWARE, PERF_COUNT_SW_DUMMY); }
> +duration_time					{ return sym(yyscanner, PERF_TYPE_SOFTWARE, PERF_COUNT_SW_DUMMY); }

not ideal to actualy create an kernel event for something we
need only access in userspace, but I could live with that..


>  bpf-output					{ return sym(yyscanner, PERF_TYPE_SOFTWARE, PERF_COUNT_SW_BPF_OUTPUT); }
>  
>  	/*
> diff --git a/tools/perf/util/stat-shadow.c b/tools/perf/util/stat-shadow.c
> index 122f37b38a65..34ae2960730b 100644
> --- a/tools/perf/util/stat-shadow.c
> +++ b/tools/perf/util/stat-shadow.c
> @@ -641,11 +641,20 @@ static void generic_metric(const char *metric_expr,
>  	expr__add_id(&pctx, name, avg);
>  	for (i = 0; metric_events[i]; i++) {
>  		struct saved_value *v;
> +		struct stats *stats;
> +		double scale;
>  
> -		v = saved_value_lookup(metric_events[i], cpu, false);
> -		if (!v)
> -			break;
> -		expr__add_id(&pctx, metric_events[i]->name, avg_stats(&v->stats));
> +		if (!strcmp(metric_events[i]->name, "duration_time")) {
> +			stats = &walltime_nsecs_stats;
> +			scale = 1e-9;

however this will enable the event value only for metric processing
and following stat command will return 0:

[jolsa@krava perf]$ ./perf stat -e duration_time kill
kill: not enough arguments

 Performance counter stats for 'kill':

                 0      duration_time:u                                             

       0.006556409 seconds time elapsed

perhaps we could substitute the value when we read the event

also walltime_nsecs_stats is only updated at the end of the
workload, so this won't work for interval.. but not sure this
is an issue though

jirka