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SubjectRe: [PATCH] perf stat: Skip duration_time in setup_system_wide
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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
>

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