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, 11 insertions, 0 deletions

diff --git a/init/main.c b/init/main.c
index 7e117a231af1..c1f999a3cf31 100644
--- a/init/main.c
+++ b/init/main.c
@@ -539,6 +539,15 @@ void __init __weak thread_info_cache_init(void)
 {
 }
 
+void __init __weak arch_early_irq_init(void)
+{
+}
+
+void __init __weak early_irq_init(void)
+{
+        arch_early_irq_init();
+}
+
 asmlinkage void __init start_kernel(void)
 {
         char * command_line;
@@ -603,6 +612,8 @@ asmlinkage void __init start_kernel(void)
         sort_main_extable();
         trap_init();
         rcu_init();
+        /* init some links before init_ISA_irqs() */
+        early_irq_init();
         init_IRQ();
         pidhash_init();
         init_timers();