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From:   Christophe JAILLET <christophe.jaillet@wanadoo.fr>
To:     Davidlohr Bueso <dave@stgolabs.net>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Neeraj Upadhyay <quic_neeraju@quicinc.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Zqiang <qiang.zhang1211@gmail.com>
Cc:     linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org,
        Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        rcu@vger.kernel.org
Subject: [PATCH] refscale: Optimize process_durations()
Date:   Sat, 28 Oct 2023 19:04:44 +0200
Message-Id: <bbbab32e3e104bdc2238724a6a4a85e539f49ddd.1698512661.git.christophe.jaillet@wanadoo.fr>
MIME-Version: 1.0
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Precedence: bulk

process_durations() is not a hot path, but there is no good reason to
iterate over and over the data already in 'buf'.

Using a seq_buf saves some useless strcat() and the need of a temp buffer.
Data is written directly at the correct place.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
 kernel/rcu/refscale.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index 2c2648a3ad30..861485d865ec 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -28,6 +28,7 @@
 #include <linux/rcupdate_trace.h>
 #include <linux/reboot.h>
 #include <linux/sched.h>
+#include <linux/seq_buf.h>
 #include <linux/spinlock.h>
 #include <linux/smp.h>
 #include <linux/stat.h>
@@ -890,31 +891,36 @@ static u64 process_durations(int n)
 {
 	int i;
 	struct reader_task *rt;
-	char buf1[64];
+	struct seq_buf s;
 	char *buf;
 	u64 sum = 0;
 
 	buf = kmalloc(800 + 64, GFP_KERNEL);
 	if (!buf)
 		return 0;
-	buf[0] = 0;
+
+	seq_buf_init(&s, buf, 800 + 64);
+
 	sprintf(buf, "Experiment #%d (Format: <THREAD-NUM>:<Total loop time in ns>)",
 		exp_idx);
 
 	for (i = 0; i < n && !torture_must_stop(); i++) {
 		rt = &(reader_tasks[i]);
-		sprintf(buf1, "%d: %llu\t", i, rt->last_duration_ns);
 
 		if (i % 5 == 0)
-			strcat(buf, "\n");
-		if (strlen(buf) >= 800) {
+			seq_buf_putc(&s, '\n');
+
+		if (seq_buf_used(&s) >= 800) {
+			seq_buf_terminate(&s);
 			pr_alert("%s", buf);
-			buf[0] = 0;
+			seq_buf_clear(&s);
 		}
-		strcat(buf, buf1);
+
+		seq_buf_printf(&s, "%d: %llu\t", i, rt->last_duration_ns);
 
 		sum += rt->last_duration_ns;
 	}
+	seq_buf_terminate(&s);
 	pr_alert("%s\n", buf);
 
 	kfree(buf);
-- 
2.34.1