linux-kernel - Re: [PATCH] perf top: Fix a race in callchain handling

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Message-ID: <20120506183212.GB2485@infradead.org>
Date:	Sun, 6 May 2012 15:32:12 -0300
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@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH] perf top: Fix a race in callchain handling

Em Sun, May 06, 2012 at 11:25:07AM +0900, Namhyung Kim escreveu:
> 2012-05-05 (토), 20:53 -0300, Arnaldo Carvalho de Melo:
> > I'm looking how to get that fixed with Peter concerns addressed.
> > 
> 
> I guess it's gonna be a non-trivial job. As far as I can see, the hists
> code can handle up to two concurrent threads regardless of the callchain
> cursor problem. And also guess that other areas of libperf also doesn't
> support the true concurrency, right?

Right, but making it even less concurrent is something we should avoid
8-)

How about this one instead? At least we would be able to, concurrently,
process multiple, unrelated hists:


diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
index 9f6d630..c5cde92 100644
--- a/tools/perf/util/hist.c
+++ b/tools/perf/util/hist.c
@@ -397,8 +397,8 @@ static bool hists__collapse_insert_entry(struct hists *hists,
 			iter->period += he->period;
 			iter->nr_events += he->nr_events;
 			if (symbol_conf.use_callchain) {
-				callchain_cursor_reset(&hists->callchain_cursor);
-				callchain_merge(&hists->callchain_cursor, iter->callchain,
+				callchain_cursor_reset(&hists->callchain_collapse_cursor);
+				callchain_merge(&hists->callchain_collapse_cursor, iter->callchain,
 						he->callchain);
 			}
 			hist_entry__free(he);
diff --git a/tools/perf/util/hist.h b/tools/perf/util/hist.h
index cfc64e2..e04c80b 100644
--- a/tools/perf/util/hist.h
+++ b/tools/perf/util/hist.h
@@ -69,6 +69,7 @@ struct hists {
 	u16			col_len[HISTC_NR_COLS];
 	/* Best would be to reuse the session callchain cursor */
 	struct callchain_cursor	callchain_cursor;
+	struct callchain_cursor	callchain_collapse_cursor;
 };
 
 struct hist_entry *__hists__add_entry(struct hists *self,
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