linux-kernel - Re: [PATCH] perf stat: Skip duration_time in setup_system

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Date:   Tue, 22 Sep 2020 15:02:18 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Jin Yao <yao.jin@...ux.intel.com>
Cc:     jolsa@...nel.org, peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, Linux-kernel@...r.kernel.org,
        ak@...ux.intel.com, kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH] perf stat: Skip duration_time in setup_system_wide

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@...co 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@...co ~]# perf stat -v -M DRAM_BW_Use -- sleep 1
  Using CPUID GenuineIntel-6-8E-A
  metric expr 64 * ( arb@...nt\=0x81\,umask\=0x1@ + arb@...nt\=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@...co ~]#

After:

  [root@...co ~]# 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@...co ~]#

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")

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

- Arnaldo