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Subject[PATCH] printk: Shrink printk_sched buffer size, eliminate it when !CONFIG_PRINTK
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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@perches.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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