Currently, the 'weight' field in the perf sample has latency information
for some instructions like in memory accesses.  And perf tool has 'weight'
and 'local_weight' sort keys to display the info.

But it's somewhat confusing what it shows exactly.  In my understanding,
'local_weight' shows a weight in a single sample, and (global) 'weight'
shows a sum of the weights in the hist_entry.

For example:

  $ perf mem record -t load dd if=/dev/zero of=/dev/null bs=4k count=1M

  $ perf report --stdio -n -s +local_weight
  ...
  #
  # Overhead  Samples  Command  Shared Object     Symbol                     Local Weight
  # ........  .......  .......  ................  .........................  ............
  #
      21.23%      313  dd       [kernel.vmlinux]  [k] lockref_get_not_zero   32
      12.43%      183  dd       [kernel.vmlinux]  [k] lockref_get_not_zero   35
      11.97%      159  dd       [kernel.vmlinux]  [k] lockref_get_not_zero   36
      10.40%      141  dd       [kernel.vmlinux]  [k] lockref_put_return     32
       7.63%      113  dd       [kernel.vmlinux]  [k] lockref_get_not_zero   33
       6.37%       92  dd       [kernel.vmlinux]  [k] lockref_get_not_zero   34
       6.15%       90  dd       [kernel.vmlinux]  [k] lockref_put_return     33
  ...

So let's look at the 'lockref_get_not_zero' symbols.  The top entry
shows that 313 samples were captured with 'local_weight' 32, so the
total weight should be 313 x 32 = 10016.  But it's not the case:

  $ perf report --stdio -n -s +local_weight,weight -S lockref_get_not_zero
  ...
  #
  # Overhead  Samples  Command  Shared Object     Local Weight  Weight
  # ........  .......  .......  ................  ............  ......
  #
       1.36%        4  dd       [kernel.vmlinux]  36            144
       0.47%        4  dd       [kernel.vmlinux]  37            148
       0.42%        4  dd       [kernel.vmlinux]  32            128
       0.40%        4  dd       [kernel.vmlinux]  34            136
       0.35%        4  dd       [kernel.vmlinux]  36            144
       0.34%        4  dd       [kernel.vmlinux]  35            140
       0.30%        4  dd       [kernel.vmlinux]  36            144
       0.30%        4  dd       [kernel.vmlinux]  34            136
       0.30%        4  dd       [kernel.vmlinux]  32            128
       0.30%        4  dd       [kernel.vmlinux]  32            128
  ...

With the 'weight' sort key, it's divided to 4 samples even with the same
info ('comm', 'dso', 'sym' and 'local_weight').  I don't think this is
what we want.

I found this because of the way it aggregates the 'weight' value.  Since
it's not a period, we should not add them in the he->stat.  Otherwise,
two 32 'weight' entries will create a 64 'weight' entry.

After that, new 32 'weight' samples don't have a matching entry so it'd
create a new entry and make it a 64 'weight' entry again and again.
Later, they will be merged into 128 'weight' entries during the
hists__collapse_resort() with 4 samples, multiple times like above.

Let's keep the weight and display it differently.  For 'local_weight',
it can show the weight as is, and for (global) 'weight' it can display
the number multiplied by the number of samples.

With this change, I can see the expected numbers.

  $ perf report --stdio -n -s +local_weight,weight -S lockref_get_not_zero
  ...
  #
  # Overhead  Samples  Command  Shared Object     Local Weight  Weight
  # ........  .......  .......  ................  ............  .....
  #
      21.23%      313  dd       [kernel.vmlinux]  32            10016
      12.43%      183  dd       [kernel.vmlinux]  35            6405
      11.97%      159  dd       [kernel.vmlinux]  36            5724
       7.63%      113  dd       [kernel.vmlinux]  33            3729
       6.37%       92  dd       [kernel.vmlinux]  34            3128
       4.17%       59  dd       [kernel.vmlinux]  37            2183
       0.08%        1  dd       [kernel.vmlinux]  269           269
       0.08%        1  dd       [kernel.vmlinux]  38            38
Reviewed-by: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20211105225617.151364-1-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>