It calculates IPC from the cycles and instruction counts and compares it
with the shadow stat for both global aggregation (default) and no
aggregation mode.

 $ perf stat -a -A -e cycles,instructions sleep 1

   Performance counter stats for 'system wide':

  CPU0   39,580,880      cycles
  CPU1   45,426,945      cycles
  CPU2   31,151,685      cycles
  CPU3   55,167,421      cycles
  CPU0   17,073,564      instructions      #    0.43  insn per cycle
  CPU1   34,955,764      instructions      #    0.77  insn per cycle
  CPU2   15,688,459      instructions      #    0.50  insn per cycle
  CPU3   34,699,217      instructions      #    0.63  insn per cycle

       1.003275495 seconds time elapsed

In this example, the 'insn per cycle' should be matched to the number
for each cpu.  For CPU2, 0.50 = 15,688,459 / 31,151,685 .

Committer testing:

  # perf test shadow
  78: perf stat metrics (shadow stat) test                            : Ok
  #
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20201127041404.390276-2-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>