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

Arnaldo Carvalho de Melo
2020-09-22T18:02:23Z

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")

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

- Arnaldo