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, 2 insertions, 1 deletions

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index 10b5092e9bfe..8e4fce4a1b1f 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -24,9 +24,10 @@
  */
 void dynamic_irq_init(unsigned int irq)
 {
-        struct irq_desc *desc = irq_to_desc(irq);
+        struct irq_desc *desc;
         unsigned long flags;
 
+        desc = irq_to_desc(irq);
         if (!desc) {
                 WARN(1, KERN_ERR "Trying to initialize invalid IRQ%d\n", irq);
                 return;