linux-kernel - Re: [PATCH v2 1/2] libperf: Add processing to scale the counters obtained during the read() system call when multiplexing

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Message-ID: <YUuhe7e0J0PSea+b@krava>
Date:   Wed, 22 Sep 2021 23:34:51 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Shunsuke Nakamura <nakamura.shun@...itsu.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        namhyung@...nel.org, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2 1/2] libperf: Add processing to scale the counters
 obtained during the read() system call when multiplexing

On Wed, Sep 22, 2021 at 07:16:26PM +0900, Shunsuke Nakamura wrote:
> From: nakamura shunsuke <nakamura.shun@...itsu.com>
> 
> perf_evsel__read() scales counters obtained by RDPMC during multiplexing, but
> does not scale counters obtained by read() system call.
> 
> Add processing to perf_evsel__read() to scale the counters obtained during the
> read() system call when multiplexing.
> 
> 
> Signed-off-by: Shunsuke Nakamura <nakamura.shun@...itsu.com>
> ---
>  tools/lib/perf/evsel.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/tools/lib/perf/evsel.c b/tools/lib/perf/evsel.c
> index 8441e3e1aaac..0ebd1d34436f 100644
> --- a/tools/lib/perf/evsel.c
> +++ b/tools/lib/perf/evsel.c
> @@ -18,6 +18,7 @@
>  #include <sys/ioctl.h>
>  #include <sys/mman.h>
>  #include <asm/bug.h>
> +#include <linux/math64.h>
>  
>  void perf_evsel__init(struct perf_evsel *evsel, struct perf_event_attr *attr,
>  		      int idx)
> @@ -321,6 +322,11 @@ int perf_evsel__read(struct perf_evsel *evsel, int cpu, int thread,
>  	if (readn(*fd, count->values, size) <= 0)
>  		return -errno;
>  
> +	if (count->ena != count->run) {
> +		if (count->run != 0)
> +			count->val = mul_u64_u64_div64(count->val, count->ena, count->run);
> +	}

so I think perf stat expect raw values in there and does the
scaling by itself, please check following code:

read_counters
  read_affinity_counters
    read_counter_cpu
      read_single_counter
        evsel__read_counter

  perf_stat_process_counter
    process_counter_maps
      process_counter_values
        perf_counts_values__scale


perhaps we could export perf_counts_values__scale if it'd be any help

jirka


> +
>  	return 0;
>  }
>  
> -- 
> 2.27.0
>