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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 21 Mar 2013 19:01:05 +0100
Subject: printk: Drop the logbuf_lock more often
The lock is hold with irgs off. The latency drops 500us+ on my arm bugs
with a "full" buffer after executing "dmesg" on the shell.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/printk/printk.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1396,6 +1396,7 @@ static int syslog_print_all(char __user
{
char *text;
int len = 0;
+ int attempts = 0;
text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
if (!text)
@@ -1407,6 +1408,14 @@ static int syslog_print_all(char __user
u64 seq;
u32 idx;
enum log_flags prev;
+ int num_msg;
+try_again:
+ attempts++;
+ if (attempts > 10) {
+ len = -EBUSY;
+ goto out;
+ }
+ num_msg = 0;
/*
* Find first record that fits, including all following records,
@@ -1422,6 +1431,14 @@ static int syslog_print_all(char __user
prev = msg->flags;
idx = log_next(idx);
seq++;
+ num_msg++;
+ if (num_msg > 5) {
+ num_msg = 0;
+ raw_spin_unlock_irq(&logbuf_lock);
+ raw_spin_lock_irq(&logbuf_lock);
+ if (clear_seq < log_first_seq)
+ goto try_again;
+ }
}
/* move first record forward until length fits into the buffer */
@@ -1435,6 +1452,14 @@ static int syslog_print_all(char __user
prev = msg->flags;
idx = log_next(idx);
seq++;
+ num_msg++;
+ if (num_msg > 5) {
+ num_msg = 0;
+ raw_spin_unlock_irq(&logbuf_lock);
+ raw_spin_lock_irq(&logbuf_lock);
+ if (clear_seq < log_first_seq)
+ goto try_again;
+ }
}
/* last message fitting into this dump */
@@ -1475,6 +1500,7 @@ static int syslog_print_all(char __user
clear_seq = log_next_seq;
clear_idx = log_next_idx;
}
+out:
raw_spin_unlock_irq(&logbuf_lock);
kfree(text);
|
