Re: [RFC] perf: EBNF for event syntax

[Masami Hiramatsu]

(2011/03/28 16:58), Peter Zijlstra wrote:
> On Mon, 2011-03-28 at 14:40 +0900, Masami Hiramatsu wrote:
>> (2011/03/25 20:07), Peter Zijlstra wrote:
>>> On Wed, 2011-03-23 at 11:36 +0800, Lin Ming wrote:
>>>> Hi, all
>>>>
>>>> On Thu, Mar 17, 2011 at 2:02 AM, Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
>>>>> How about we start writing proper EBNF syntax rules for this stuff, its
>>>>> getting seriously out of hand.
>>>> http://marc.info/?l=linux-kernel&m=130029871318866&w=2
>>>>
>>>> As Peter suggested, I wrote a simple EBNF for event syntax, as below.
>>>> My first plan is to pass in extra config value for some events,
>>>> for example, offcore response and load latency.
>>>>
>>>> perf record -e r100b(0004):p
>>>>
>>>> As above, the extra config value 0004 is passed in the parentheses.
>>>>
>>>> The EBNF
>>>> ========
>>>>
>>>> EventList		:=	Event [',' EventList]
>>>
>>> There was a suggestion a while back to make:
>>>
>>>  -e ev1,ev2,ev3
>>>
>>> create an event group with ev2 and ev3 siblings of ev1, and have
>>> multiple -e instances create separate counters.
>>>
>>> The problem is that its not backwards compatible, but something like
>>> that would still be very nice to have.
>>
>> I doubt that we really need to define those events are
>> grouped at recording time, because group(event ratio)
>> analysis must be done at analysis time(report etc.)
> 
> Uhm, grouping isn't at all related to event ratios, you can do event
> ratios just fine without groups - there's some stronger correlation when
> you do ratios with groups, but since its all statistics anyway, you can
> get that same extra correlation by simply running longer too.
> 
> Groups are most useful in measuring events on another base, which is
> basically mandatory if your primary event doesn't have sampling support
> itself.

Ah, OK, there are some arch/events don't have a sampling mode.
If I understand it correctly, how about below syntax?

-e (ev2,ev3)/ev1

This create an event group with ev2 and ev3 siblings of ev1 (and
ev1 gives sampling base).

Thank you,

-- 
Masami HIRAMATSU
2nd Dept. Linux Technology Center
Hitachi, Ltd., Systems Development Laboratory
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx
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