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, 13 insertions, 1 deletions

diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h
index 4a145caeee07..4ee4b3d2316f 100644
--- a/include/linux/kernel_stat.h
+++ b/include/linux/kernel_stat.h
@@ -28,7 +28,9 @@ struct cpu_usage_stat {
 
 struct kernel_stat {
         struct cpu_usage_stat   cpustat;
-        unsigned int irqs[NR_IRQS];
+#ifndef CONFIG_SPARSE_IRQ
+       unsigned int irqs[NR_IRQS];
+#endif
 };
 
 DECLARE_PER_CPU(struct kernel_stat, kstat);
@@ -39,6 +41,10 @@ DECLARE_PER_CPU(struct kernel_stat, kstat);
 
 extern unsigned long long nr_context_switches(void);
 
+#ifndef CONFIG_SPARSE_IRQ
+#define kstat_irqs_this_cpu(irq) \
+        (kstat_this_cpu.irqs[irq])
+
 struct irq_desc;
 
 static inline void kstat_incr_irqs_this_cpu(unsigned int irq,
@@ -46,11 +52,17 @@ static inline void kstat_incr_irqs_this_cpu(unsigned int irq,
 {
         kstat_this_cpu.irqs[irq]++;
 }
+#endif
+
 
+#ifndef CONFIG_SPARSE_IRQ
 static inline unsigned int kstat_irqs_cpu(unsigned int irq, int cpu)
 {
        return kstat_cpu(cpu).irqs[irq];
 }
+#else
+extern unsigned int kstat_irqs_cpu(unsigned int irq, int cpu);
+#endif
 
 /*
  * Number of interrupts per specific IRQ source, since bootup