As of now it doesn't consider cgroups when collecting shadow stats and
metrics so counter values from different cgroups will be saved in a same
slot. This resulted in incorrect numbers when those cgroups have
different workloads.
For example, let's look at the scenario below: cgroups A and C runs same
workload which burns a cpu while cgroup B runs a light workload.
$ perf stat -a -e cycles,instructions --for-each-cgroup A,B,C sleep 1
Performance counter stats for 'system wide':
3,958,116,522 cycles A
6,722,650,929 instructions A # 2.53 insn per cycle
1,132,741 cycles B
571,743 instructions B # 0.00 insn per cycle
4,007,799,935 cycles C
6,793,181,523 instructions C # 2.56 insn per cycle
1.001050869 seconds time elapsed
When I run 'perf stat' with single workload, it usually shows IPC around
1.7. We can verify it (6,722,650,929.0 / 3,958,116,522 = 1.698) for cgroup A.
But in this case, since cgroups are ignored, cycles are averaged so it
used the lower value for IPC calculation and resulted in around 2.5.
avg cycle: (3958116522 + 1132741 + 4007799935) / 3 = 2655683066
IPC (A) : 6722650929 / 2655683066 = 2.531
IPC (B) : 571743 / 2655683066 = 0.0002
IPC (C) : 6793181523 / 2655683066 = 2.557
We can simply compare cgroup pointers in the evsel and it'll be NULL
when cgroups are not specified. With this patch, I can see correct
numbers like below:
$ perf stat -a -e cycles,instructions --for-each-cgroup A,B,C sleep 1
Performance counter stats for 'system wide':
4,171,051,687 cycles A
7,219,793,922 instructions A # 1.73 insn per cycle
1,051,189 cycles B
583,102 instructions B # 0.55 insn per cycle
4,171,124,710 cycles C
7,192,944,580 instructions C # 1.72 insn per cycle
1.007909814 seconds time elapsed
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jin Yao <yao.jin@linux.intel.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/20210115071139.257042-2-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
a1bf23052b