[PATCH 2/4] irq: allocate irq_desc_ptrs array based on nr_irqs

Mike Travis
2009-01-10T22:39:56Z

[-- Attachment #1: irq-alloc-irq_ptrs --]
[-- Type: text/plain, Size: 2351 bytes --]

Impact: preparation for making irq_desc_ptrs variable-sized.

This addresses this memory usage bump when NR_CPUS bumped from 128 to 4096:

34816 +229376 264192 +658% irq_desc_ptrs(.data.read_mostly)

The patch is split into two part, the first simply allocates the
irq_desc_ptrs array. Then next will deal with making it variable.
This is only when CONFIG_SPARSE_IRQS=y.

Signed-off-by: Mike Travis <travis@sgi.com>
---
kernel/irq/handle.c | 11 +++++++++--
kernel/irq/internals.h | 4 ++++
2 files changed, 13 insertions(+), 2 deletions(-)

--- linux-2.6-for-ingo.orig/kernel/irq/handle.c
+++ linux-2.6-for-ingo/kernel/irq/handle.c
@@ -17,6 +17,7 @@
#include <linux/kernel_stat.h>
#include <linux/rculist.h>
#include <linux/hash.h>
+#include <linux/bootmem.h>

#include "internals.h"

@@ -110,7 +111,7 @@ static void init_one_irq_desc(int irq, s
*/
DEFINE_SPINLOCK(sparse_irq_lock);

-struct irq_desc *irq_desc_ptrs[NR_IRQS] __read_mostly;
+struct irq_desc **irq_desc_ptrs __read_mostly;

static struct irq_desc irq_desc_legacy[NR_IRQS_LEGACY] __cacheline_aligned_in_smp = {
[0 ... NR_IRQS_LEGACY-1] = {
@@ -137,6 +138,9 @@ int __init early_irq_init(void)
desc = irq_desc_legacy;
legacy_count = ARRAY_SIZE(irq_desc_legacy);

+ /* allocate irq_desc_ptrs array based on nr_irqs */
+ irq_desc_ptrs = alloc_bootmem(nr_irqs * sizeof(void *));
+
for (i = 0; i < legacy_count; i++) {
desc[i].irq = i;
desc[i].kstat_irqs = kstat_irqs_legacy[i];
@@ -153,7 +157,10 @@ int __init early_irq_init(void)

struct irq_desc *irq_to_desc(unsigned int irq)
{
- return (irq < nr_irqs) ? irq_desc_ptrs[irq] : NULL;
+ if (irq_desc_ptrs && irq < nr_irqs)
+ return irq_desc_ptrs[irq];
+
+ return NULL;
}

struct irq_desc *irq_to_desc_alloc_cpu(unsigned int irq, int cpu)
--- linux-2.6-for-ingo.orig/kernel/irq/internals.h
+++ linux-2.6-for-ingo/kernel/irq/internals.h
@@ -16,7 +16,11 @@ extern int __irq_set_trigger(struct irq_
extern struct lock_class_key irq_desc_lock_class;
extern void init_kstat_irqs(struct irq_desc *desc, int cpu, int nr);
extern spinlock_t sparse_irq_lock;
+#ifdef CONFIG_SPARSE_IRQ
+extern struct irq_desc **irq_desc_ptrs;
+#else
extern struct irq_desc *irq_desc_ptrs[NR_IRQS];
+#endif

#ifdef CONFIG_PROC_FS
extern void register_irq_proc(unsigned int irq, struct irq_desc *desc);

--