linux-kernel - SPARSE

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Message-ID: <20121219072211.GE2939@squish.home.loc>
Date:	Wed, 19 Dec 2012 02:22:11 -0500
From:	Paul Thompson <set.mailinglist@...il.com>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: SPARSE_IRQ

	Hi;

	Perhaps Im being an idiot, but it looks to me like the
menu-item for SPARSE_IRQ (under General setup -> IRQ subsystem)
depends solely on MAY_HAVE_SPARSE_IRQ, but I only see *one* user
for that in the kernel now, the SuperH arch (arch/sh/Kconfig). It
looks like everyone else explicitly sets SPARSE_IRQ. However the
menu-items description implies it is a more generic option...
	It seems like this menu item used to appear, in a forced
on state, then this condition made it disapear, leaving a blank
IRQ subsystem menu for me. I was trying to work around that, but
now, I am not sure exactly what is supposed to be going on here...

Paul

(from kernel/irq/Kconfig)
config SPARSE_IRQ
        bool "Support sparse irq numbering" if MAY_HAVE_SPARSE_IRQ
        ---help---

          Sparse irq numbering is useful for distro kernels that want
          to define a high CONFIG_NR_CPUS value but still want to have
          low kernel memory footprint on smaller machines.

          ( Sparse irqs can also be beneficial on NUMA boxes, as they spread
            out the interrupt descriptors in a more NUMA-friendly way. )

          If you don't know what to do here, say N.

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