Re: [PATCH] perf stat: Skip duration_time in setup_system_wide

[Jin, Yao]

Hi Arnaldo,

On 9/23/2020 2:02 AM, Arnaldo Carvalho de Melo wrote:

Em Tue, Sep 22, 2020 at 02:56:30PM -0300, Arnaldo Carvalho de Melo escreveu:

Em Tue, Sep 22, 2020 at 09:50:04AM +0800, Jin Yao escreveu:

Some metrics (such as DRAM_BW_Use) consists of uncore events and
duration_time. For uncore events, counter->core.system_wide is
true. But for duration_time, counter->core.system_wide is false
so target.system_wide is set to false.

Then 'enable_on_exec' is set in perf_event_attr of uncore event.
Kernel will return error when trying to open the uncore event.

This patch skips the duration_time in setup_system_wide then
target.system_wide will be set to true for the evlist of uncore
events + duration_time.

Before (tested on skylake desktop):

  # perf stat -M DRAM_BW_Use -- sleep 1
  Error:
  The sys_perf_event_open() syscall returned with 22 (Invalid argument) for 
event (arb/event=0x84,umask=0x1/).
  /bin/dmesg | grep -i perf may provide additional information.

After:

  # perf stat -M DRAM_BW_Use -- sleep 1

   Performance counter stats for 'system wide':

                 169      arb/event=0x84,umask=0x1/ #     0.00 DRAM_BW_Use
              40,427      arb/event=0x81,umask=0x1/
       1,000,902,197 ns   duration_time

         1.000902197 seconds time elapsed

Fixes: 648b5af3f3ae ("libperf: Move 'system_wide' from 'struct evsel' to 'struct 
perf_evsel'")

Humm, what makes you think that this cset was the one introducing this
problem? It just moves evsel->system_wide to evsel->core.system_wide.

Apart from that I reproduced the problem and after applying your patch
it seems cured:

   [acme@quaco perf]$ grep 'model name' -m1 /proc/cpuinfo
   model name   : Intel(R) Core(TM) i7-8650U CPU @ 1.90GHz

Before (with -v to see details):

   [root@quaco ~]# perf stat -v -M DRAM_BW_Use -- sleep 1
   Using CPUID GenuineIntel-6-8E-A
   metric expr 64 * ( arb@event\=0x81\,umask\=0x1@ + 
arb@event\=0x84\,umask\=0x1@ ) / 1000000 / duration_time / 1000 for DRAM_BW_Use
   found event duration_time
   found event arb/event=0x84,umask=0x1/
   found event arb/event=0x81,umask=0x1/
   adding {arb/event=0x84,umask=0x1/,arb/event=0x81,umask=0x1/}:W,duration_time
   Control descriptor is not initialized
   Warning:
   arb/event=0x84,umask=0x1/ event is not supported by the kernel.
   Error:
   The sys_perf_event_open() syscall returned with 22 (Invalid argument) for 
event (arb/event=0x84,umask=0x1/).
   /bin/dmesg | grep -i perf may provide additional information.

[root@quaco ~]#

After:

   [root@quaco ~]# perf stat -M DRAM_BW_Use -- sleep 1

Performance counter stats for 'system wide': 2,806 arb/event=0x84,umask=0x1/ # 0.63 DRAM_BW_Use

           10,001,820      arb/event=0x81,umask=0x1/
        1,016,875,686 ns   duration_time

1.016875686 seconds time elapsed [root@quaco ~]#

So I'm removing that fixes and adding this one, that I think is where
"duration_time" was being considered...

Fixes: e3ba76deef23064f ("perf tools: Force uncore events to system wide 
monitoring")

Yes, this fixes is much better, thanks.

Also, wouldn't it be better to have the duration_time event with its
evsel->core.system_wide set to true?

That looks to be another solution, should be OK too I think. :)

But anyway we need a test.

Thanks
Jin Yao

- Arnaldo