linux-kernel - [PATCH 3/3] tracing: simplify printf'ing in seq_print

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Message-Id: <20181026211347.2442-3-linux@rasmusvillemoes.dk>
Date:   Fri, 26 Oct 2018 23:13:46 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] tracing: simplify printf'ing in seq_print_sym

trace_seq_printf(..., "%s", ...) can be done with trace_seq_puts()
instead, avoiding printf overhead. In the second instance, the string
we're copying was just created from an snprintf() to a stack buffer, so
we might as well do that printf directly. This naturally leads to moving
the declaration of the str buffer inside the CONFIG_KALLSYMS guard,
which in turn will make gcc inline the function for !CONFIG_KALLSYMS (it
only has a single caller, but the huge stack frame seems to make gcc not
inline it for CONFIG_KALLSYMS).

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 kernel/trace/trace_output.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 7417ce5fe4bb..0f96262d23be 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -341,8 +341,8 @@ static inline const char *kretprobed(const char *name)
 static void
 seq_print_sym(struct trace_seq *s, unsigned long address, bool with_offset)
 {
-	char str[KSYM_SYMBOL_LEN];
 #ifdef CONFIG_KALLSYMS
+	char str[KSYM_SYMBOL_LEN];
 	const char *name;
 
 	if (with_offset)
@@ -352,12 +352,11 @@ seq_print_sym(struct trace_seq *s, unsigned long address, bool with_offset)
 	name = kretprobed(str);
 
 	if (name && strlen(name)) {
-		trace_seq_printf(s, "%s", name);
+		trace_seq_puts(s, name);
 		return;
 	}
 #endif
-	snprintf(str, KSYM_SYMBOL_LEN, "0x%08lx", address);
-	trace_seq_printf(s, "%s", str);
+	trace_seq_printf(s, "0x%08lx", address);
 }
 
 #ifndef CONFIG_64BIT
-- 
2.19.1.6.gbde171bbf5