linux-kernel - Re: [PATCH] perf/tools : remove default system

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Date:   Wed, 25 Oct 2017 19:03:17 +0800
From:   "chengjian (D)" <cj.chengjian@...wei.com>
To:     Namhyung Kim <namhyung@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
CC:     <peterz@...radead.org>, <mingo@...hat.com>,
        <alexander.shishkin@...ux.intel.com>,
        <linux-kernel@...r.kernel.org>, <linux-perf-users@...r.kernel.org>,
        <xiexiuqi@...wei.com>, <huawei.libin@...wei.com>,
        <zhangmengting@...wei.com>, <kernel-team@....com>
Subject: Re: [PATCH] perf/tools : remove default system_wide in sched record



On 2017/10/25 10:23, Namhyung Kim wrote:
> On Tue, Oct 24, 2017 at 10:46:44AM -0300, Arnaldo Carvalho de Melo wrote:
>> Em Tue, Oct 24, 2017 at 03:45:34PM +0800, Cheng Jian escreveu:
>>> When running perf sched record, there is a bug.
>>>
>>> It's system_wide when we specify a command line.
>> Humm, isn't this because if you trace just a workload you will miss the
>> sched-in events?
>>
>> Perhaps with PERF_RECORD_SWITCH we can solve that... I.e. still get the
>> sched-in events while tracing just one workload, not requiring
>> system_wide like it is the case now, right?
> Yes, but it will lose other task's comm, also (at least) sched-wakeup
> (from other task) events are still needed.
>
> Thanks,
> Namhyung
>

I found that if the parameters -p and -a were specified at the same time,
PID/TID(-p/-t) would overwrite SYSTEM_WIDE (-a) in target__validate( ).

If we don't specify a process(-p) or a workload, it will make system 
wide (-a)
as the default target.

     /* Make system wide (-a) the default target. */
     if (!argc && target__none(&rec->opts.target))
         rec->opts.target.system_wide = true;

So don't -a and -p should have the same operation and feedback?

It also lose some events when use -p.