linux-kernel - Re: [PATCH 1/4] perf trace: Improve error message when receive non-tracepoint events

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Date:	Sat, 9 Apr 2016 00:12:41 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	<pi3orama@....com>, <linux-kernel@...r.kernel.org>,
	<lizefan@...wei.com>, Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH 1/4] perf trace: Improve error message when receive
 non-tracepoint events



On 2016/4/8 23:22, Arnaldo Carvalho de Melo wrote:
> Em Fri, Apr 08, 2016 at 03:07:22PM +0000, Wang Nan escreveu:
>> Before this patch, strange error message is provided if passed a
>> non-tracepoint event to 'perf trace':
>>
>>   # perf trace -a  --ev cycles sleep 1
>>   Failed to set filter "common_pid != 27500" on event cycles with 22 (Invalid argument)
>>
>> This is because 'perf trace' accepts all valid events during cmdline
>> parsing, but in fact user can only provide tracepoints, because it
>> needs filter.
>>
>> This patch validate evlist, report error earlier:
>>
>>   # ./perf trace -a  --ev cycles sleep 1
>>   Only support tracepoint events!
> Humm, perhaps we should instead refrain from setting filters to non
> tracepoint events? I.e. I don't see why we whouldn't support, say,
> software events...
>
> /me trying some now, i.e.:
>
>    # trace --ev minor-faults --no-syscalls
>
> But it has some issues...
>
> - Arnaldo
>   

We already have commit fdf14720fbd02 ("perf tools: Only set filter for
tracepoints events") so you won't see the ugly error message again.

However, I think parsing non-tracepoint events in 'perf trace' is still
a challange. We never support it in 'perf trace' and I'm not too much
sure who will need this feature and how to use them, and why he/she can't
use 'perf record' instead.

Thank you.