Messages in this thread | | | Date | Fri, 8 Mar 2019 11:00:16 +0100 | From | Petr Mladek <> | Subject | Re: [RFC PATCH v1 00/25] printk: new implementation |
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On Thu 2019-03-07 10:53:48, John Ogness wrote: > On 2019-03-04, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> wrote: > > If there are setups which can be fully !atomic (in terms of console > > output) then we, essentially, have a fully preemptible kthread printk > > implementation. > > Correct. I've mentioned in another response[0] some ideas about what > could be done to aid this. > > I understand that fully preemptible kthread printing is unacceptable for > you. Since all current console drivers are already irq safe, I'm > wondering if using irq_work to handle the emergency printing for console > drivers without write_atomic() would help. (If the printk caller is in a > context that write() supports, then write() could be called directly.) > This would also demand that the irq-safe requirements for write() are > not relaxed. The printk-kthread might still be faster than irq_work, but > it might increase reliability if an irq_work is triggered as an extra > precaution.
It is getting more and more complicated. The messages would be pushed directly, from irq, and kthread. It would depend how the code would look like but I am not much optimistic.
Note that you could not pass any data to the irq_work handler. It would need to iterate over the logbuffer and take care of all non-handled emergency messages.
Anyway, we could solve this later. We need to keep the current console_unlock() handling as a fallback until enough consoles support the direct mode anyway.
Best Regards, Petr
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