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From b4bf7654e00cd7da0d18577698e25eb199de2d57 Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 21 Mar 2013 19:01:05 +0100
Subject: [PATCH 208/347] printk: Drop the logbuf_lock more often
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.246-rt110.tar.xz
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 | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 273f2c7864b5..1e0988a0bb97 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1457,12 +1457,23 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
u64 next_seq;
u64 seq;
u32 idx;
+ int attempts = 0;
+ int num_msg;
text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
if (!text)
return -ENOMEM;
logbuf_lock_irq();
+
+try_again:
+ attempts++;
+ if (attempts > 10) {
+ len = -EBUSY;
+ goto out;
+ }
+ num_msg = 0;
+
/*
* Find first record that fits, including all following records,
* into the user-provided buffer for this dump.
@@ -1475,6 +1486,14 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
len += msg_print_text(msg, true, NULL, 0);
idx = log_next(idx);
seq++;
+ num_msg++;
+ if (num_msg > 5) {
+ num_msg = 0;
+ logbuf_unlock_irq();
+ logbuf_lock_irq();
+ if (clear_seq < log_first_seq)
+ goto try_again;
+ }
}
/* move first record forward until length fits into the buffer */
@@ -1486,6 +1505,14 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
len -= msg_print_text(msg, true, NULL, 0);
idx = log_next(idx);
seq++;
+ num_msg++;
+ if (num_msg > 5) {
+ num_msg = 0;
+ logbuf_unlock_irq();
+ logbuf_lock_irq();
+ if (clear_seq < log_first_seq)
+ goto try_again;
+ }
}
/* last message fitting into this dump */
@@ -1523,6 +1550,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
clear_seq = log_next_seq;
clear_idx = log_next_idx;
}
+out:
logbuf_unlock_irq();
kfree(text);
--
2.36.1
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