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

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Date:   Tue, 23 Jan 2018 15:40:33 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     "Jin, Yao" <yao.jin@...ux.intel.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 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