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

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Date:	Thu, 22 Oct 2015 15:29:16 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Namhyung Kim <namhyung@...nel.org>
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 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?

> Thanks,
> Namhyung


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