Re: [PATCH v8 4/4] printk: allow increasing the ring buffer depending on the number of CPUs

["Luis R. Rodriguez" <mcgrof@suse.com>]

On Fri, Jun 27, 2014 at 04:59:14PM -0700, Andrew Morton wrote:
> On Thu, 26 Jun 2014 16:32:15 -0700 "Luis R. Rodriguez" <mcgrof@suse.com> wrote:
> 
> > On Thu, Jun 26, 2014 at 4:20 PM, Andrew Morton
> > <akpm@linux-foundation.org> wrote:
> > > On Fri, 27 Jun 2014 01:16:30 +0200 "Luis R. Rodriguez" <mcgrof@suse.com> wrote:
> > >
> > >> > > Another note --  since this option depends on SMP and !BASE_SMALL technically
> > >> > > num_possible_cpus() won't ever return something smaller than or equal to 1
> > >> > > but because of the default values chosen the -1 on the compuation does affect
> > >> > > whether or not this will trigger on > 64 CPUs or >= 64 CPUs, keeping the
> > >> > > -1 means we require > 64 CPUs.
> > >> >
> > >> > hm, that sounds like more complexity.
> > >> >
> > >> > > This all can be changed however we like but the language and explained logic
> > >> > > would just need to be changed.
> > >> >
> > >> > Let's start out simple.  What's wrong with doing
> > >> >
> > >> >     log buf len = max(__LOG_BUF_LEN, nr_possible_cpus * per-cpu log buf len)
> > >>
> > >> Sure, you already took in the patch series though so how would you like to
> > >> handle a respin, you just drop the last patch and we respin it?
> > >
> > > A fresh patch would suit.  That's if you think it is a reasonable
> > > approach - you've thought about this stuff more than I have!
> > 
> > The way its implemented now makes more technical sense, in short it
> > assumes the first boot (and CPU) gets the full default kernel ring
> > buffer size, the extra size is for the gibberish that each extra CPU
> > is expected to spew out in the worst case. What you propose makes the
> > explanation simpler and easier to understand but sends the wrong
> > message about exactly how the growth of the kernel ring buffer is
> > expected scale with the addition of more CPUs.
> 
> OK, it's finally starting to sink in.  The model for the kernel-wide
> printk output is "a great pile of CPU-independent stuff plus a certain
> amount of per-cpu stuff".  And the code at present attempts to follow
> that model.  Yes?

Yup, exactly.

> I'm rather internet-challenged at present - please let me take another look at
> the patch on Monday.

OK!

  Luis