Re: [RFC][PATCHv6 00/12] printk: introduce printing kernel thread

Sergey Senozhatsky
2017-12-19T02:46:17Z

On (12/18/17 21:03), Steven Rostedt wrote:
> > and this is exactly what I'm still observing. i_do_printks-1992 stops
> > printing, while console_sem is owned by another task. Since log_store()
> > much faster than call_console_drivers() AND console_sem owner is getting
> > preempted for unknown period of time, we end up having pending messages
> > in logbuf... and it's kworker/0:1-135 that prints them all.
> >
> > systemd-udevd-671 [003] d..3 66.334866: offloading: set console_owner
> > kworker/0:1-135 [000] d..2 66.335999: offloading: vprintk_emit()->trylock FAIL will spin? :1
> > i_do_printks-1992 [002] d..2 66.345474: offloading: vprintk_emit()->trylock FAIL will spin? :0 x 1100
> > ...
> > systemd-udevd-671 [003] d..3 66.345917: offloading: clear console_owner waiter != NULL :1
>
> And kworker will still be bounded in what it can print. Yes it may end
> up being the entire buffer, but that should not take longer than a
> watchdog.

not the case on my setup. "1100 messages" is already longer than watchdog.
consoles don't scale. if anyone's console can keep up with 2 printing CPUs,
then let's see what logbuf size that person will set on a system with 1024
CPUs under OOM. I doubt that will be 128KB.

anyway,
before you guys push the patch to printk.git, can we wait for Tejun to
run his tests against it? (or do we have a preemptive "non realistic
tests" conclusion?)

-ss