Re: [PATCH 6/6] powerpc: Enable sparse irq_descs on powerpc

[Michael Ellerman <michael@ellerman.id.au>]

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On Wed, 2009-10-14 at 12:44 -0600, Grant Likely wrote:
> On Tue, Oct 13, 2009 at 11:45 PM, Michael Ellerman
> <michael@ellerman.id.au> wrote:
> > Defining CONFIG_SPARSE_IRQ enables generic code that gets rid of the
> > static irq_desc array, and replaces it with an array of pointers to
> > irq_descs.
> >
> > It also allows node local allocation of irq_descs, however we
> > currently don't have the information available to do that, so we just
> > allocate them on all on node 0.
> >
> > Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
> 
> Why not make sparse IRQs manditory for all platforms?  Is there a
> performance concern with doing so?  From a maintenance perspective,
> I'd rather see IRQ descs manged in one way only to keep the code
> simple.

I agree on the maintenance angle. My thinking was we'd run with it
optional but default y for a release or two, and if no one complains we
can make it mandatory.

It does make some code paths bigger, and looking up an irq_desc is going
to take slightly more cycles. I don't think it's a big issue, but I
thought we should try it for a while before making it mandatory. The
code has only been tested on x86 and sh as far as I know.

cheers

ps. thanks for the review

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