Re: [Ksummit-discuss] Late KS topics

[David Woodhouse <dwmw2@infradead.org>]

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On Mon, 2015-10-26 at 15:25 +0100, Hannes Reinecke wrote:
> 
> 
> The other topic is a rather short one, which possibly could be move
> to
> a lightning talk:
> - printk usecases
>   Currently, printk is used for two largely different usecases:
>   1) Really urgent, 'ship me out at any cost now' messages
>   and
>   2) Rather longish, 'and incidentally I always wanted to tell
>   you what I did on my recent holidays' type of logging entries.
>   As it so happens, this really makes it hard to do any improvements
>   for printk as it inevitably messes up one or the other side.
>   (This whole idea came up as we've had some instances which simply
>    could not boot as the serial console took too long to print out
>    all the stuff, so systemd timeout kicked in and killed the udev
>    process which should have handled the boot device.)
>   The talk/proposal should be used to come to a consensus about
>   restricting printk() to high-priority, small volume messages,
>   and implement a different call (like log_printk()) for the
>   low-priority, high-volume traffic.

Currently, the former doesn't work. As lamented recently, there's no
synchronous printk even over serial console any more. It's lossy, and
you can't even do the traditional printk debugging any more with
   printk(); is_this_the_bit_that_kills_the_machine(); printk(); 
because the first printk might not be *seen* before the machine dies.

-- 
dwmw2



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