linux-kernel - Re: [PATCH] perf util: Use target->per_thread and target->system

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Date:   Wed, 24 Jan 2018 08:12:33 +0800
From:   "Jin, Yao" <yao.jin@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        jolsa@...nel.org, Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH] perf util: Use target->per_thread and target->system_wide
 flags



On 1/23/2018 10:40 PM, Jiri Olsa wrote:
> On Tue, Jan 23, 2018 at 07:02:44AM +0800, Jin, Yao wrote:
> 
> SNIP
> 
>>>>           threads = thread_map__new_str(target->pid, target->tid, target->uid,
>>>> -                                     target->per_thread);
>>>> +                                     target->per_thread && target->system_wide);
>>>
>>> At first glance I thought your solution would do the trick but perf
>>> record does use target->system_wide when the '-a' switch is used.
>>> Moreover specifying the '-a' switch doesn't prevent the '--per-thread'
>>> option from being used as well, making both target->perf_thread and
>>> target_system_wide equal to true (and that is not good).
>>>
>>> Although not a fan of adding more to struct target, the advantage of
>>> having target->all_threads is that we are guaranteed that it isn't
>>> used anywhere else.
>>>
>>> Let me know what you think,
>>> Mathieu
>>>
>>
>> If we specify both '-a' and '--per-thread' to perf record, perf record will
>> override'--per-thread'. So now target->per_thread = false, and
>> target->system_wide = true.
>>
>> If we specify '--per-thread' only to perf record, target->per_thread = true,
>> and target->system_wide = false.
>>
>> So whatever for any case, target->per_thread && target->system_wide is
>> false.
>>
>> Since the parameter is false, in thread_map__new_str(), it will not execute
>> the thread_map__new_all_cpus(). So that will not change perf record previous
>> behavior.
>>
>> In perf stat, it allows the case that target->per_thread and
>> target->system_wide are all true. That means we want to collect system-wide
>> per-thread metrics.
> 
> could you please put this description into comment
> before the thread_map__new_str is called?
> 
> thanks,
> jirka
> 

OK, I will put this comment in v2. I will send v2 soon.

Thanks
Jin Yao