linux-kernel - Re: [PATCH 1/5] perf top: Use active evsel for non-sample events on old kernel

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Message-ID: <4F273651.2020908@gmail.com>
Date:	Tue, 31 Jan 2012 09:31:13 +0900
From:	Namhyung Kim <namhyung@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] perf top: Use active evsel for non-sample events
 on old kernel

2012-01-31 3:55 AM, Arnaldo Carvalho de Melo wrote:
> Em Sun, Jan 29, 2012 at 05:55:52PM +0900, Namhyung Kim escreveu:
>> If multiple events are specified on old kernel,
>> perf_evlist__id2evsel() returns NULL for non-sampling events
>> since the sample.id doesn't contain valid value, and it triggers
>> assert below. If only one event is given, the function returns
>> the evsel regardless of sample.id, this is why most case cause
>> no problem on old kernel.
>>
>> Fix it by using active evsel.
>
> How about this one instead:
>
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index a6d50e3..3ffb320 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -349,6 +349,10 @@ struct perf_evsel *perf_evlist__id2evsel(struct perf_evlist *evlist, u64 id)
>   	hlist_for_each_entry(sid, pos, head, node)
>   		if (sid->id == id)
>   			return sid->evsel;
> +
> +	if (!perf_evlist__sample_id_all(evlist))
> +		return list_entry(evlist->entries.next, struct perf_evsel, node);
> +
>   	return NULL;
>   }
>
> That way we won't have to patch other tools that would get the same
> problem in such new tool/old kernel combos, right?
>

Right, looks good to me.


> Do you see any problem with not checking the header type?
>

No, I don't, at least for now :)


> Also please try to avoid using perf_session fields, prefer to use
> perf_{evlist,evsel} when possible, in this case you could use
> perf_evlist__sample_id_all(evlist), for instance.
>
> - Arnaldo
>

OK, will do that later.

Thanks,
Namhyung
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