Re: [PATCH] panic.c: export panic_on_oops

Ingo Molnar
2009-10-12T12:20:40Z

* David Woodhouse <dwmw2@infradead.org> wrote:

> On Mon, 2009-10-12 at 14:09 +0200, Ingo Molnar wrote:
> > Also, would it be possible to just simplify the thing and not do any
> > buffering at all? Extra buffering complexity in a console driver is only
> > asking for trouble. Or is flash storage write cycles optimization that
> > important in this case?
>
> That and the fact that on NAND flash you have to write full pages at a
> time -- that's 512 bytes, 2KiB or 4KiB depending on the type of chip.
> So we really do want to buffer it where we can.
>
> We don't want to write a 2KiB page for every line of printk output.

Then i think the buffering is at the wrong place: we should instead
buffer in the generic layer and pass it to lowlevel if we know that we
have gone past a 2K boundary.

The size of the generic log buffer is always a power of two so detecting
2K boundaries is very easy. On any emergency the generic console layer
will do faster flushes - this is nothing the console driver itself
should bother with.

And that would avoid the whole workqueue logic - which is fragile to be
done in a printk to begin with.

So what we need is an extension to struct console that sets a buffering
limit. Zero (the default) means unbuffered.

(Btw., things like netconsole might make use of such buffering too.)

Agreed?

Ingo