linux-kernel - Re: [PATCH 26/31] perf tools: Support perf event alias name

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Date:	Thu, 22 Oct 2015 16:53:14 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	"Wangnan (F)" <wangnan0@...wei.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Daniel Borkmann <daniel@...earbox.net>,
	David Ahern <dsahern@...il.com>, He Kuang <hekuang@...wei.com>,
	Jiri Olsa <jolsa@...nel.org>, Li Zefan <lizefan@...wei.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Paul Mackerras <paulus@...ba.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	pi3orama <pi3orama@....com>,
	xiakaixu 00238161 <xiakaixu@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 26/31] perf tools: Support perf event alias name

On Thu, Oct 22, 2015 at 4:29 PM, Wangnan (F) <wangnan0@...wei.com> wrote:
>
>
> On 2015/10/22 15:16, Namhyung Kim wrote:
>>
>> Hi,
>>
>> On Wed, Oct 21, 2015 at 10:00 PM, Wangnan (F) <wangnan0@...wei.com> wrote:
>>>
>>>
>>> On 2015/10/21 16:53, Namhyung Kim wrote:
>>>>
>>>> Hi,
>>>>
>>>> On Wed, Oct 14, 2015 at 12:41:37PM +0000, Wang Nan wrote:
>>>>>
>>>>> From: He Kuang <hekuang@...wei.com>
>>>>>
>>>>> This patch adds new bison rules for specifying an alias name to a perf
>>>>> event, which allows cmdline refer to previous defined perf event
>>>>> through
>>>>> its name. With this patch user can give alias name to a perf event
>>>>> using
>>>>> following cmdline:
>>>>>
>>>>>    # perf record -e mypmu=cycles ...
>>>>>
>>>>> To allow parser refer to existing event selecter, pass event list to
>>>>> 'struct parse_events_evlist'. perf_evlist__find_evsel_by_alias() is
>>>>> introduced to get evsel through its alias.
>>>>
>>>> What about using event name directly?  I guess the alias name is used
>>>> only to refer an event so it'd be better to use the event name.
>>>> Anyway we need alias as well when event has no name or name is complex.
>>>
>>>
>>> It is possible to trigger two perf events with same PMU but
>>> different config options:
>>>
>>>   # perf record -e cycles/period=9999/ -e cycles/period=99999/ -a sleep 1
>>>
>>> In this case the name of events are:
>>>
>>> cycles/period=9999/ `
>>> cycles/period=99999/
>>>
>>> Using it in perf cmdline is painful:
>>>
>>>   # perf record -e cycles/period=9999/ -e cycles/period=99999/ -e
>>> bpf_program.c/myevent=cycles/period=9999//...
>>
>> I understand the need of using aliases but I think it's more natural
>> to use event name for simple cases..
>
>
> I will consider this. However, if we allow using event name directly like
> this:
>
>  # perf record -e cycles -e test_pmu.c/myevent=cycles/ ...
>
> Then two '-e' seems redundant, right? Why not directly using:
>
>  # perf record -e test_pmu.c/myevent=cycles/ ...
>
> and make perf creates cycles event for test_pmu.c?
>
> We can make syntax like
>
>  # perf record -e test_pmu.c/myevent=cycles/ ...
>
> as a syntax sugar of
>
>  # perf record -e randomname=cycles -e test_pmu.c/myevent=randomname/ ...
>
> and don't need to find evsel through their names if alias not exist.
>
> So this is a new feature, and worth another patch.
>
> Thought?

Not sure it's worth.  It can confuse users IMHO.

Isn't it enough to give them in a single argument?

  # perf record -e cycles,test_pmu.c/myevent=cycles/

Thanks,
Namhyung
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