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