sparse irq_desc[] array: core kernel and x86 changes

Impact: new feature

Problem on distro kernels: irq_desc[NR_IRQS] takes megabytes of RAM with
NR_CPUS set to large values. The goal is to be able to scale up to much
larger NR_IRQS value without impacting the (important) common case.

To solve this, we generalize irq_desc[NR_IRQS] to an (optional) array of
irq_desc pointers.

When CONFIG_SPARSE_IRQ=y is used, we use kzalloc_node to get irq_desc,
this also makes the IRQ descriptors NUMA-local (to the site that calls
request_irq()).

This gets rid of the irq_cfg[] static array on x86 as well: irq_cfg now
uses desc->chip_data for x86 to store irq_cfg.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 10 insertions, 0 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ac22bb7719f7..48ac688de3cd 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -238,6 +238,16 @@ config X86_HAS_BOOT_CPU_ID
         def_bool y
         depends on X86_VOYAGER
 
+config SPARSE_IRQ
+        bool "Support sparse irq numbering"
+        depends on PCI_MSI || HT_IRQ
+        default y
+        help
+          This enables support for sparse irq, esp for msi/msi-x. You may need
+          if you have lots of cards supports msi-x installed.
+
+          If you don't know what to do here, say Y.
+
 config X86_FIND_SMP_CONFIG
         def_bool y
         depends on X86_MPPARSE || X86_VOYAGER