Hi Jirka

quoted

On Wed, Sep 22, 2021 at 07:16:26PM +0900, Shunsuke Nakamura wrote:

quoted

From: nakamura shunsuke <redacted>

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 <redacted>
---
 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

quoted

@@ -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

Thank you for your comment.

The purpose of this patch is to unify the counters obtained with
perf_evsel__read() to scaled or unscaled values.

perf_evsel__read() gets counter by perf_mmap__read_self() if RDPMC is
available, else gets by readn(). In current implementation, caller
gets scaled counter if goes through RDPMC path, otherwise gets unscaled
counter via readn() path.

However caller cannnot know which path were taken.

If caller expects a raw value, I think the RDPMC path should also
return an unscaled counter.

diff --git a/tools/lib/perf/mmap.c b/tools/lib/perf/mmap.c
index c89dfa5..aaa4579 100644
--- a/tools/lib/perf/mmap.c
+++ b/tools/lib/perf/mmap.c

@@ -353,8 +353,6 @@ int perf_mmap__read_self(struct perf_mmap *map, struct perf_counts_values *count
                count->ena += delta;
                if (idx)
                        count->run += delta;
-
-               cnt = mul_u64_u64_div64(cnt, count->ena, count->run);
        }

        count->val = cnt;

Rob, do you have any comments?