linux-kernel - Re: [PATCH v5 08/14] perf tools: Support perf event alias name

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Message-ID: <20151215131834.GB31734@krava.brq.redhat.com>
Date:	Tue, 15 Dec 2015 14:18:34 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	acme@...nel.org, masami.hiramatsu.pt@...achi.com, jolsa@...nel.org,
	linux-kernel@...r.kernel.org, pi3orama@....com, lizefan@...wei.com,
	He Kuang <hekuang@...wei.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH v5 08/14] perf tools: Support perf event alias name

On Mon, Dec 14, 2015 at 10:39:17AM +0000, Wang Nan wrote:
> From: He Kuang <hekuang@...wei.com>
> 
> This patch is useful when trying to pass a perf event to BPF map.
> Before this patch we are unable to pass an event with config term to
> BPF maps. For example:
> 
>  # perf record -a -e cycles/no-inherit,period=0x7fffffffffffffff/ \
>                   -e './test_bpf_map_2.c/maps:pmu_map.event=cycles/no-inherit,period=0x7fffffffffffffff//' ls /
>  event syntax error: '..ps:pmu_map.event=cycles/'
>                                    \___ Event not found for map setting
> 
> Because those '/' and ',' embarrass parser.

we already have 'name=' term, but it's only for pmu events,
so I think your solution is better

> 
> 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. The above goal can be achieved using:
> 
>  # perf record -a -e cyc=cycles/no-inherit,period=0x7fffffffffffffff/ \
>                   -e './test_bpf_map_2.c/maps:pmu_map.event=cyc/' ls /
> 

so this alias should only help as a quick pointer
to setup the record session, right?

I'm not sure we want to see it as a part of name being stored
to perf.data and displayed by perf report and stat

  $ ./perf stat -e cyc=cycles ls

    Performance counter stats for 'ls':

         2,638,646      cyc=cycles                                                  

       0.001111614 seconds time elapsed

but I guess when you probably have a reason to use that
you want to see it in your report..  just a thought ;-)

anyway acking the change

Acked-by: Jiri Olsa <jolsa@...nel.org>

thanks,
jirka
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