linux-kernel - [PATCH] seq_file: Optimize seq

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Message-Id: <5c4f7ad7b88f5026940efa9c8be36a58755ec1b3.1704374916.git.christophe.jaillet@wanadoo.fr>
Date: Thu,  4 Jan 2024 14:29:37 +0100
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Jan Kara <jack@...e.cz>
Cc: linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org,
	Christophe JAILLET <christophe.jaillet@...adoo.fr>,
	linux-fsdevel@...r.kernel.org
Subject: [PATCH] seq_file: Optimize seq_puts()

Most of seq_puts() usages are done with a string literal. In such cases,
the length of the string car be computed at compile time in order to save
a strlen() call at run-time. seq_write() can then be used instead.

This saves a few cycles.

To have an estimation of how often this optimization triggers:
   $ git grep seq_puts.*\" | wc -l
   3391

Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
Checked by comparing the output of a few .s files.
Here is one of these outputs:

$ diff -u drivers/clk/clk.s.old drivers/clk/clk.s | grep -C6 seq_w

 	call	clk_prepare_unlock	#
 # drivers/clk/clk.c:3320: 	seq_puts(s, "}\n");
 	movq	%r12, %rdi	# s,
+	movl	$2, %edx	#,
 	movq	$.LC66, %rsi	#,
-	call	seq_puts	#
+	call	seq_write	#
 	call	__tsan_func_exit	#
 # drivers/clk/clk.c:3322: }
 	xorl	%eax, %eax	#
@@ -34520,6 +34521,7 @@
 	popq	%rbp	#
 	popq	%r12	#
--
 # drivers/clk/clk.c:3205: 		seq_puts(s, "-----");
 	call	__sanitizer_cov_trace_pc	#
+	movl	$5, %edx	#,
 	movq	$.LC72, %rsi	#,
 	movq	%r13, %rdi	# s,
-	call	seq_puts	#
+	call	seq_write	#
 	jmp	.L2134	#
 .L2144:
 # drivers/clk/clk.c:1793: 	return clk_core_get_accuracy_no_lock(core);
@@ -35225,20 +35228,23 @@
 	leaq	240(%r12), %rdi	#, tmp95
 	call	__tsan_read8	#
--
 	movq	%r12, %rdi	# s,
+	movq	$.LC77, %rsi	#,
 # drivers/clk/clk.c:3244: 	struct hlist_head **lists = s->private;
 	movq	240(%r12), %rbp	# s_9(D)->private, lists
 # drivers/clk/clk.c:3246: 	seq_puts(s, "                                 enable  prepare  protect                                duty  hardware                            connection\n");
-	call	seq_puts	#
+	call	seq_write	#
 # drivers/clk/clk.c:3247: 	seq_puts(s, "   clock                          count    count    count        rate   accuracy phase  cycle    enable   consumer                         id\n");
+	movl	$142, %edx	#,
 	movq	$.LC78, %rsi	#,
 	movq	%r12, %rdi	# s,
-	call	seq_puts	#
+	call	seq_write	#
 # drivers/clk/clk.c:3248: 	seq_puts(s, "---------------------------------------------------------------------------------------------------------------------------------------------\n");
+	movl	$142, %edx	#,
 	movq	$.LC79, %rsi	#,
 	movq	%r12, %rdi	# s,
-	call	seq_puts	#
+	call	seq_write	#
 # drivers/clk/clk.c:3251: 	clk_prepare_lock();
 	call	clk_prepare_lock	#
 .L2207:
@@ -37511,7 +37517,7 @@
 	subq	$16, %rsp	#,
 # drivers/clk/clk.c:3082: {
---
 fs/seq_file.c            |  4 ++--
 include/linux/seq_file.h | 10 +++++++++-
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/fs/seq_file.c b/fs/seq_file.c
index f5fdaf3b1572..8ef0a07033ca 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -669,7 +669,7 @@ void seq_putc(struct seq_file *m, char c)
 }
 EXPORT_SYMBOL(seq_putc);
 
-void seq_puts(struct seq_file *m, const char *s)
+void __seq_puts(struct seq_file *m, const char *s)
 {
 	int len = strlen(s);
 
@@ -680,7 +680,7 @@ void seq_puts(struct seq_file *m, const char *s)
 	memcpy(m->buf + m->count, s, len);
 	m->count += len;
 }
-EXPORT_SYMBOL(seq_puts);
+EXPORT_SYMBOL(__seq_puts);
 
 /**
  * seq_put_decimal_ull_width - A helper routine for putting decimal numbers
diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
index 234bcdb1fba4..15abf45d62c5 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -118,7 +118,15 @@ void seq_vprintf(struct seq_file *m, const char *fmt, va_list args);
 __printf(2, 3)
 void seq_printf(struct seq_file *m, const char *fmt, ...);
 void seq_putc(struct seq_file *m, char c);
-void seq_puts(struct seq_file *m, const char *s);
+void __seq_puts(struct seq_file *m, const char *s);
+#define seq_puts(m, s)						\
+do {								\
+	if (__builtin_constant_p(s))				\
+		seq_write(m, s, __builtin_strlen(s));		\
+	else							\
+		__seq_puts(m, s);				\
+} while (0)
+
 void seq_put_decimal_ull_width(struct seq_file *m, const char *delimiter,
 			       unsigned long long num, unsigned int width);
 void seq_put_decimal_ull(struct seq_file *m, const char *delimiter,
-- 
2.34.1