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

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Date:   Wed, 23 Sep 2020 10:05:56 +0800
From:   "Jin, Yao" <yao.jin@...ux.intel.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
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

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@...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")
> 

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
>