From a89e96532d76b48402b32b6ed9b3e928a6431e10 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Thu, 21 Mar 2013 19:01:05 +0100 Subject: [PATCH 249/352] 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. Change-Id: I825444cb8aa3c3e582aec9c4957ec680c9ae2b15 Signed-off-by: Sebastian Andrzej Siewior --- kernel/printk/printk.c | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 7938094..b737ec8 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1395,6 +1395,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear) { char *text; int len = 0; + int attempts = 0; text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL); if (!text) @@ -1406,6 +1407,14 @@ static int syslog_print_all(char __user *buf, int size, bool clear) 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, @@ -1421,6 +1430,14 @@ static int syslog_print_all(char __user *buf, int size, bool clear) prev = msg->flags; 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 */ @@ -1434,6 +1451,14 @@ static int syslog_print_all(char __user *buf, int size, bool clear) prev = msg->flags; 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 */ @@ -1474,6 +1499,7 @@ 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); -- 2.7.4