linux-kernel - [PATCH 2/9] perf top: Access hists->lock only if needed

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Date:	Fri, 11 Dec 2015 11:22:25 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Namhyung Kim <namhyung@...nel.org>,
	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 2/9] perf top: Access hists->lock only if needed

From: Namhyung Kim <namhyung@...nel.org>

The perf_top__record_precise_ip() releases and regrabs the
he->hists->lock because it can sleep if there's an error.  But it should
be done conditionally as it slows down the fast path.

Signed-off-by: Namhyung Kim <namhyung@...nel.org>
Cc: David Ahern <dsahern@...il.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Link: http://lkml.kernel.org/r/1449802616-16170-2-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/builtin-top.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 3b0978e5578a..586798acf7db 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -194,21 +194,23 @@ static void perf_top__record_precise_ip(struct perf_top *top,
 
 	pthread_mutex_unlock(&notes->lock);
 
-	/*
-	 * This function is now called with he->hists->lock held.
-	 * Release it before going to sleep.
-	 */
-	pthread_mutex_unlock(&he->hists->lock);
+	if (unlikely(err)) {
+		/*
+		 * This function is now called with he->hists->lock held.
+		 * Release it before going to sleep.
+		 */
+		pthread_mutex_unlock(&he->hists->lock);
+
+		if (err == -ERANGE && !he->ms.map->erange_warned)
+			ui__warn_map_erange(he->ms.map, sym, ip);
+		else if (err == -ENOMEM) {
+			pr_err("Not enough memory for annotating '%s' symbol!\n",
+			       sym->name);
+			sleep(1);
+		}
 
-	if (err == -ERANGE && !he->ms.map->erange_warned)
-		ui__warn_map_erange(he->ms.map, sym, ip);
-	else if (err == -ENOMEM) {
-		pr_err("Not enough memory for annotating '%s' symbol!\n",
-		       sym->name);
-		sleep(1);
+		pthread_mutex_lock(&he->hists->lock);
 	}
-
-	pthread_mutex_lock(&he->hists->lock);
 }
 
 static void perf_top__show_details(struct perf_top *top)
-- 
2.1.0

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