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Date: Tue, 24 Jun 2014 02:20:50 +0200
From: "Luis R. Rodriguez" <mcgrof@suse.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>, gregkh@linuxfoundation.org,
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        Kees Cook <keescook@chromium.org>, Davidlohr Bueso <davidlohr@hp.com>,
        Chris Metcalf <cmetcalf@tilera.com>
Subject: Re: [PATCH v8 4/4] printk: allow increasing the ring buffer
	depending on the number of CPUs
Message-ID: <20140624002050.GC27687@wotan.suse.de>
References: <1403124337-14886-1-git-send-email-mcgrof@do-not-panic.com> <1403124337-14886-4-git-send-email-mcgrof@do-not-panic.com> <20140623154134.43ac7ab63896cd9ebcba84b6@linux-foundation.org>
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On Mon, Jun 23, 2014 at 03:41:34PM -0700, Andrew Morton wrote:
> On Wed, 18 Jun 2014 13:45:37 -0700 "Luis R. Rodriguez" <mcgrof@do-not-panic.com> wrote:
> 
> > ...
> >
> > If an increase is required the ring buffer is increased to
> > +	  the next power of 2 that can fit both the minimum kernel ring buffer
> > +	  (LOG_BUF_SHIFT) plus the additional worst case CPU contributions.
> >
> > ...
> >
> > +	log_buf_len_update(cpu_extra + __LOG_BUF_LEN);
> > +}
> 
> I'd have expected
> 
>   total_cpu_space = minimum-per-cpu-len * nr_possible_cpus;
>   log_buf_len = max(__LOG_BUF_LEN, total_cpu_space)
> 
> but here you added __LOG_BUF_LEN to total_cpu_space and I cannot work
> out why.  
> .

Ah, because its cpu_extra, not total_cpu_space that is being
computed, the goal was to see how much extra junk on the
worst case a CPU might contribute. The __LOG_BUF_LEN is the
default size, so we combine both.

  Luis