The problem is clear. But the big part of the problem is that printk()
tries to show the messages on all consoles immediately.
I wonder how much the per-console loglevel would be needed
when the console handling is offloaded to per-console kthreads, see
It causes that printk() should "never" block and each console might
run on its own speed.
It still might be useful from some reasons:
+ Serial consoles might miss messages because the old messages are
over-written before they reach the console. It might be solved
by big enough buffer.
+ printk() still tries to show the messages immediately in some
critical situations, for example, early boot, watchdog warnings,
suspend, reboot, OOps, panic(). The slow consoles might still
cause stalls and put the system into its knees.
+ People might need to explicitly disable the kthreads, for
example, when debugging a situation when kthreads are not
PS: I am sorry for the late response. I am still snowed under
many tasks. The printk kthreads are complicated and need
a lot of attention. Plus there was a sickness, vacations,
and other tasks.