77 lines
2.0 KiB
Diff
77 lines
2.0 KiB
Diff
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Thu, 21 Mar 2013 19:01:05 +0100
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Subject: printk: Drop the logbuf_lock more often
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.9/older/patches-4.9.20-rt16.tar.xz
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The lock is hold with irgs off. The latency drops 500us+ on my arm bugs
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with a "full" buffer after executing "dmesg" on the shell.
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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kernel/printk/printk.c | 26 ++++++++++++++++++++++++++
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1 file changed, 26 insertions(+)
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--- a/kernel/printk/printk.c
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+++ b/kernel/printk/printk.c
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@@ -1396,6 +1396,7 @@ static int syslog_print_all(char __user
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{
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char *text;
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int len = 0;
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+ int attempts = 0;
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text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
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if (!text)
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@@ -1407,6 +1408,14 @@ static int syslog_print_all(char __user
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u64 seq;
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u32 idx;
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enum log_flags prev;
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+ int num_msg;
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+try_again:
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+ attempts++;
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+ if (attempts > 10) {
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+ len = -EBUSY;
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+ goto out;
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+ }
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+ num_msg = 0;
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/*
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* Find first record that fits, including all following records,
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@@ -1422,6 +1431,14 @@ static int syslog_print_all(char __user
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prev = msg->flags;
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idx = log_next(idx);
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seq++;
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+ num_msg++;
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+ if (num_msg > 5) {
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+ num_msg = 0;
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+ raw_spin_unlock_irq(&logbuf_lock);
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+ raw_spin_lock_irq(&logbuf_lock);
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+ if (clear_seq < log_first_seq)
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+ goto try_again;
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+ }
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}
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/* move first record forward until length fits into the buffer */
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@@ -1435,6 +1452,14 @@ static int syslog_print_all(char __user
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prev = msg->flags;
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idx = log_next(idx);
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seq++;
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+ num_msg++;
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+ if (num_msg > 5) {
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+ num_msg = 0;
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+ raw_spin_unlock_irq(&logbuf_lock);
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+ raw_spin_lock_irq(&logbuf_lock);
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+ if (clear_seq < log_first_seq)
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+ goto try_again;
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+ }
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}
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/* last message fitting into this dump */
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@@ -1475,6 +1500,7 @@ static int syslog_print_all(char __user
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clear_seq = log_next_seq;
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clear_idx = log_next_idx;
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}
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+out:
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raw_spin_unlock_irq(&logbuf_lock);
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kfree(text);
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