linux-kernel - Re: [PATCH] x86_64: resize NR_IRQS for large machines (re-submit)

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Date:	Wed, 26 Mar 2008 23:24:51 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Alan Mayer <ajm@....com>
Cc:	torvalds@...ux-foundation.org,
	linux-kernel list <linux-kernel@...r.kernel.org>,
	Robin Holt <holt@....com>, Jack Steiner <steiner@....com>,
	Russ Anderson <rja@....com>
Subject: Re: [PATCH] x86_64: resize NR_IRQS for large machines (re-submit)


* Alan Mayer <ajm@....com> wrote:

> > but it doesnt really depart from the current status quo of huge 
> > [NR_IRQS] arrays either. Patches that make NR_IRQS a variable are 
> > welcome :)
> 
> Good luck with that.  If i come up with something that's elegant 
> enough to make it worth the risk, I'll let you know.  Changing NR_IRQS 
> to a variable touches every arch and a lot of drivers.  Someone is 
> bound to choke on it, so it has to be something worth fighting for.

well, i dont it has to be (or it should be) an all or nothing patch, 
given the complexity and risks involved.

- we should first introduce a nr_irqs variable and a Kconfig switch 
  (say CONFIG_ARCH_HAS_DYNAMIC_NR_IRQS) for architectures to toggle. If 
  the switch is toggled, nr_irqs is a variable, otherwise it's a carbon 
  copy of NR_IRQS. Some array-definition, declaration and initialization 
  wrappers are provided as well.

- then the core code, x86 and most drivers can be converted to nr_irqs.
  The switch might initially even be user-selectable if
  CONFIG_DEBUG_KERNEL, to ease regression testing.

- other architectures will follow one by one, fixing their
  arch-dependent drivers as well in the process

- finally we get rid of the wrappers.

	Ingo
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