On (03/07/16 11:52), Jan Kara wrote: [..] > So for UP systems, we should by default disable async printing anyway I > suppose. It is just a pointless overhead. So please just make printk_sync > default to true if !CONFIG_SMP.
ok, thanks. > When IRQs are disabled, you're right we will have a change in behavior. I > don't see an easy way of avoiding delaying of printk until IRQs get > enabled. I don't want to queue work directly because that creates > possibility for lock recursion in queue_work(). And playing some tricks > with irq_works isn't easy either - you cannot actually rely on any other > CPU doing anything (even a timer tick) because of NOHZ. yes. I thought about some sort of PRINTK_IPI on smp, and queue work from PRINTK_IPI. which is a bit insane. > So if this will be a problem in practice, using a kthread will probably be > the easiest solution. probably kthread is the way to go then. Tetsuo's bad experience with workqueues also sounds a bit alarming. I'll post a new patch soon. -ss