linux-kernel - [PATCH] printk: Shrink printk_sched buffer size, eliminate it when !CONFIG

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Date:	Tue, 29 May 2012 11:17:11 -0700
From:	Joe Perches <joe@...ches.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kay Sievers <kay@...y.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] printk: Shrink printk_sched buffer size, eliminate it when
 !CONFIG_PRINTK

The size of the per-cpu printk_sched buf is much larger
than necessary.  The maximum sched message emitted is
~80 bytes. Shrink the allocation for this printk_sched
buffer from 512 bytes to 128.

printk_sched creates an unnecessary per-cpu buffer when
CONFIG_PRINTK is not enabled.  Remove it when appropriate
so embedded uses save a bit of space too.

Signed-off-by: Joe Perches <joe@...ches.com>
---
 kernel/printk.c |   14 ++++++++++----
 1 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/kernel/printk.c b/kernel/printk.c
index 32462d2..61cff0b 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -1726,24 +1726,30 @@ int is_console_locked(void)
 }
 
 /*
- * Delayed printk version, for scheduler-internal messages:
+ * Delayed printk version, for scheduler-internal messages.
+ * Not the normal 512 as it's a bit wasteful, sched messages are short,
+ * and 128 is more than sufficient for all current messages.
  */
-#define PRINTK_BUF_SIZE		512
+#define PRINTK_SCHED_BUF_SIZE	128
 
 #define PRINTK_PENDING_WAKEUP	0x01
 #define PRINTK_PENDING_SCHED	0x02
 
 static DEFINE_PER_CPU(int, printk_pending);
-static DEFINE_PER_CPU(char [PRINTK_BUF_SIZE], printk_sched_buf);
+#ifdef CONFIG_PRINTK
+static DEFINE_PER_CPU(char [PRINTK_SCHED_BUF_SIZE], printk_sched_buf);
+#endif
 
 void printk_tick(void)
 {
 	if (__this_cpu_read(printk_pending)) {
 		int pending = __this_cpu_xchg(printk_pending, 0);
+#ifdef CONFIG_PRINTK
 		if (pending & PRINTK_PENDING_SCHED) {
 			char *buf = __get_cpu_var(printk_sched_buf);
 			printk(KERN_WARNING "[sched_delayed] %s", buf);
 		}
+#endif
 		if (pending & PRINTK_PENDING_WAKEUP)
 			wake_up_interruptible(&log_wait);
 	}
@@ -2189,7 +2195,7 @@ int printk_sched(const char *fmt, ...)
 	buf = __get_cpu_var(printk_sched_buf);
 
 	va_start(args, fmt);
-	r = vsnprintf(buf, PRINTK_BUF_SIZE, fmt, args);
+	r = vsnprintf(buf, PRINTK_SCHED_BUF_SIZE, fmt, args);
 	va_end(args);
 
 	__this_cpu_or(printk_pending, PRINTK_PENDING_SCHED);


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