From: Petr Mladek Date: Fri, 6 Oct 2023 10:21:51 +0200 Subject: [PATCH 084/134] printk: Reduce pr_flush() pooling time Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz pr_flush() does not guarantee that all messages would really get flushed to the console. The best it could do is to wait with a given timeout.[*] The current interval 100ms for checking the progress might seem too long in some situations. For example, such delays are not appreciated during suspend and resume especially when the consoles have been flushed "long" time before the check. On the other hand, the sleeping wait might be useful in other situations. Especially, it would allow flushing the messages using printk kthreads on the same CPU[*]. Use msleep(1) as a compromise. Also measure the time using jiffies. msleep() does not guarantee precise wakeup after the given delay. It might be much longer, especially for times < 20s. See Documentation/timers/timers-howto.rst for more details. Note that msecs_to_jiffies() already translates a negative value into an infinite timeout. [*] console_unlock() does not guarantee flushing the consoles since the commit dbdda842fe96f893 ("printk: Add console owner and waiter logic to load balance console writes"). It would be possible to guarantee it another way. For example, the spinning might be enabled only when the console_lock has been taken via console_trylock(). But the load balancing is helpful. And more importantly, the flush with a timeout has been added as a preparation step for introducing printk kthreads. Signed-off-by: Petr Mladek Reviewed-by: John Ogness Link: https://lore.kernel.org/r/20231006082151.6969-3-pmladek@suse.com Signed-off-by: Sebastian Andrzej Siewior --- kernel/printk/printk.c | 26 +++++++++++++------------- 1 file changed, 13 insertions(+), 13 deletions(-) --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3742,7 +3742,8 @@ late_initcall(printk_late_init); /* If @con is specified, only wait for that console. Otherwise wait for all. */ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { - int remaining = timeout_ms; + unsigned long timeout_jiffies = msecs_to_jiffies(timeout_ms); + unsigned long remaining_jiffies = timeout_jiffies; struct console *c; u64 last_diff = 0; u64 printk_seq; @@ -3760,6 +3761,9 @@ static bool __pr_flush(struct console *c console_unlock(); for (;;) { + unsigned long begin_jiffies; + unsigned long slept_jiffies; + diff = 0; /* @@ -3797,24 +3801,20 @@ static bool __pr_flush(struct console *c console_srcu_read_unlock(cookie); if (diff != last_diff && reset_on_progress) - remaining = timeout_ms; + remaining_jiffies = timeout_jiffies; console_unlock(); /* Note: @diff is 0 if there are no usable consoles. */ - if (diff == 0 || remaining == 0) + if (diff == 0 || remaining_jiffies == 0) break; - if (remaining < 0) { - /* no timeout limit */ - msleep(100); - } else if (remaining < 100) { - msleep(remaining); - remaining = 0; - } else { - msleep(100); - remaining -= 100; - } + /* msleep(1) might sleep much longer. Check time by jiffies. */ + begin_jiffies = jiffies; + msleep(1); + slept_jiffies = jiffies - begin_jiffies; + + remaining_jiffies -= min(slept_jiffies, remaining_jiffies); last_diff = diff; }