On Thu, 16 Nov 2006, Linus Torvalds wrote:
>
>
> On Thu, 16 Nov 2006, Alan Stern wrote:
> > On Thu, 16 Nov 2006, Linus Torvalds wrote:
> > >
> > > Paul, it would be _really_ nice to have some way to just initialize
> > > that SRCU thing statically. This kind of crud is just crazy.
> >
> > I looked into this back when SRCU was first added. It's essentially
> > impossible to do it, because the per-cpu memory allocation & usage APIs
> > are completely different for the static and the dynamic cases.
>
> I don't think that's how you'd want to do it.
>
> There's no way to do an initialization of a percpu allocation statically.
> That's pretty obvious.
Hmmm... What about DEFINE_PER_CPU in include/asm-generic/percpu.h
combined with setup_per_cpu_areas() in init/main.c? So long as you want
all the CPUs to start with the same initial values, it should work.
> What I'd suggest instead, is to make the allocation dynamic, and make it
> inside the srcu functions (kind of like I did now, but I did it at a
> higher level).
>
> Doing it at the high level was trivial right now, but we may well end up
> hitting this problem again if people start using SRCU more. Right now I
> suspect the cpufreq notifier is the only thing that uses SRCU, and it
> already showed this problem with SRCU initializers.
>
> So I was more thinking about moving my "one special case high level hack"
> down lower, down to the SRCU level, so that we'll never see _more_ of
> those horrible hacks. We'll still have the hacky thing, but at least it
> will be limited to a single place - the SRCU code itself.
Another possible approach (but equally disgusting) is to use this static
allocation approach, and have the SRCU structure include both a static and
a dynamic percpu pointer together with a flag indicating which should be
used.
Alan Stern
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