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

Jiri Olsa
2021-09-22T21:34:59Z

On Wed, Sep 22, 2021 at 07:16:26PM +0900, Shunsuke Nakamura wrote:
> From: nakamura shunsuke <nakamura.shun@fujitsu.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@fujitsu.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
>