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

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Message-ID: <20120130185532.GC15935@infradead.org>
Date:	Mon, 30 Jan 2012 16:55:32 -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 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?

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

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

> Signed-off-by: Namhyung Kim <namhyung@...il.com>
> ---
>  tools/perf/builtin-top.c |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index e8b033c074f9..f68fba52c8d8 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -771,6 +771,14 @@ static void perf_top__mmap_read_idx(struct perf_top *top, int idx)
>  		}
>  
>  		evsel = perf_evlist__id2evsel(session->evlist, sample.id);
> +		if (evsel == NULL && !session->sample_id_all &&
> +		    event->header.type != PERF_RECORD_SAMPLE) {
> +			/*
> +			 * Old kernel, no sample_id_all field.
> +			 * Just use active evsel.
> +			 */
> +			evsel = top->sym_evsel;
> +		}
>  		assert(evsel != NULL);
>  
>  		origin = event->header.misc & PERF_RECORD_MISC_CPUMODE_MASK;
> -- 
> 1.7.8.2
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