irq: initialize nr_irqs based on nr_cpu_ids

Impact: Reduce memory usage.

This is the second half of the changes to make the irq_desc_ptrs be
variable sized based on nr_cpu_ids.  This is done by adding a new
"max_nr_irqs" macro to irq_vectors.h (and a dummy in irqnr.h) to
return a max NR_IRQS value based on NR_CPUS or nr_cpu_ids.

This necessitated moving the define of MAX_IO_APICS to a separate
file (asm/apicnum.h) so it could be included without the baggage
of the other asm/apicdef.h declarations.
Signed-off-by: Mike Travis <travis@sgi.com>

arch/x86/include/asm/apicdef.h

@@ -132,12 +132,8 @@
 #define APIC_BASE_MSR	0x800
 #define X2APIC_ENABLE	(1UL << 10)
 
-#ifdef CONFIG_X86_32
-# define MAX_IO_APICS 64
-#else
-# define MAX_IO_APICS 128
-# define MAX_LOCAL_APIC 32768
-#endif
+/* get MAX_IO_APICS */
+#include <asm/apicnum.h>
 
 /*
  * All x86-64 systems are xAPIC compatible.

arch/x86/include/asm/apicnum.h

+#ifndef _ASM_X86_APICNUM_H
+#define _ASM_X86_APICNUM_H
+
+/* define MAX_IO_APICS */
+#ifdef CONFIG_X86_32
+# define MAX_IO_APICS 64
+#else
+# define MAX_IO_APICS 128
+# define MAX_LOCAL_APIC 32768
+#endif
+
+#endif /* _ASM_X86_APICNUM_H */

arch/x86/include/asm/irq_vectors.h

@@ -105,6 +105,8 @@
 
 #if defined(CONFIG_X86_IO_APIC) && !defined(CONFIG_X86_VOYAGER)
 
+#include <asm/apicnum.h>	/* need MAX_IO_APICS */
+
 #ifndef CONFIG_SPARSE_IRQ
 # if NR_CPUS < MAX_IO_APICS
 #  define NR_IRQS (NR_VECTORS + (32 * NR_CPUS))
@@ -112,11 +114,15 @@
 #  define NR_IRQS (NR_VECTORS + (32 * MAX_IO_APICS))
 # endif
 #else
-# if (8 * NR_CPUS) > (32 * MAX_IO_APICS)
-#  define NR_IRQS (NR_VECTORS + (8 * NR_CPUS))
-# else
-#  define NR_IRQS (NR_VECTORS + (32 * MAX_IO_APICS))
-# endif
+
+/* defined as a macro so nr_irqs = max_nr_irqs(nr_cpu_ids) can be used */
+# define max_nr_irqs(nr_cpus)				\
+	((8 * nr_cpus) > (32 * MAX_IO_APICS) ?		\
+		(NR_VECTORS + (8 * NR_CPUS)) :		\
+		(NR_VECTORS + (32 * MAX_IO_APICS)))	\
+
+# define NR_IRQS max_nr_irqs(NR_CPUS)
+
 #endif
 
 #elif defined(CONFIG_X86_VOYAGER)

include/linux/irqnr.h

@@ -20,11 +20,18 @@
 
 # define for_each_irq_desc_reverse(irq, desc)                          \
 	for (irq = nr_irqs - 1; irq >= 0; irq--)
+
 #else /* CONFIG_GENERIC_HARDIRQS */
 
+#include <asm/irq_vectors.h>	/* need possible max_nr_irqs() */
+
 extern int nr_irqs;
 extern struct irq_desc *irq_to_desc(unsigned int irq);
 
+# ifndef max_nr_irqs
+#  define max_nr_irqs(nr_cpus)	NR_IRQS
+# endif
+
 # define for_each_irq_desc(irq, desc)					\
 	for (irq = 0, desc = irq_to_desc(irq); irq < nr_irqs;		\
 	     irq++, desc = irq_to_desc(irq))				\

kernel/irq/handle.c

@@ -133,6 +133,9 @@ int __init early_irq_init(void)
 	int legacy_count;
 	int i;
 
+	/* initialize nr_irqs based on nr_cpu_ids */
+	nr_irqs = max_nr_irqs(nr_cpu_ids);
+
 	printk(KERN_INFO "NR_IRQS:%d nr_irqs:%d\n", NR_IRQS, nr_irqs);
 
 	desc = irq_desc_legacy;