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

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Message-ID: <20120131003423.GA25293@infradead.org>
Date:	Mon, 30 Jan 2012 22:34:23 -0200
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Namhyung Kim <namhyung@...il.com>
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

Em Tue, Jan 31, 2012 at 09:31:13AM +0900, Namhyung Kim escreveu:
> 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.

Please resend that way and I'll apply, or lemme know if you prefer for
me to do it and just stick your 'Acked-by: ' or 'Tested-by:' on it.
 
> 
> >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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