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Date: Wed, 27 Jul 2016 23:05:32 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Josh Triplett <josh@joshtriplett.org>
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Subject: Re: [Ksummit-discuss] [TECH TOPIC] asynchronous printk
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On Thu, 21 Jul 2016 07:21:28 -0700
Josh Triplett <josh@joshtriplett.org> wrote:
> 
> Given the discussion in this thread about wanting to eliminate
> earlyprintk in favor of a unified mechanism that works as early as
> possible, how would this case work on the system I described above where
> earlyprintk works and console doesn't?

No no no!!! Please do not eliminate earlyprintk(). It is critical to
the PREEMPT_RT project. It requires no sleeping locks, and can be used
in pretty much any context (with slight modifications). printk() is a
beast, and in -rt it calls sleeping locks. That is, if interrupts are
disabled, we prevent printk from print anything. (Note PREEMPT_RT
keeps interrupts enabled much more than the normal kernel does). If a
bug happens where interrupts are disabled, we fall back to earlyprintk
(and tracing), to debug it.

-- Steve