On Tue, 24 Jun 2014 03:05:54 +0200 "Luis R. Rodriguez" <mcg...@suse.com> wrote:
> > > 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.
> >
> > Well... why? Isn't it simpler and more direct to say "I want at least
> > 32k per CPU"?
>
> That's certainly another way to go about this, but the original motivation
> was trying to figure out the additional *extra* junk a CPU might spewed out,
> it set out with an assumption of a base start from the first CPU booting the
> system and that first CPU using the default kernel ring buffer size. The
> language in the patch describes the worst case extra CPU junk contributed,
> rather than a specific full split of the kernel ring buffer as that's
> typically
> how extra junk is spewered out to the ring bufer and the concern. In general
> on idle each CPU only contributes about only 1 to max 2 lines. The focus then
> is the worst case on contribution.
I don't think I understood all that ;)
> 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)
?
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