x86: arch_probe_nr_irqs

Impact: save RAM with large NR_CPUS, get smaller nr_irqs
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Mike Travis <travis@sgi.com>

arch/x86/include/asm/irq_vectors.h

@@ -115,14 +115,11 @@
 # endif
 #else
 
-/* 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) ?		\
+# define NR_IRQS					\
+	((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)

arch/x86/kernel/io_apic.c

@@ -3850,6 +3850,22 @@ void __init probe_nr_irqs_gsi(void)
 		nr_irqs_gsi = nr;
 }
 
+#ifdef CONFIG_SPARSE_IRQ
+int __init arch_probe_nr_irqs(void)
+{
+	int nr;
+
+	nr = ((8 * nr_cpu_ids) > (32 * nr_ioapics) ?
+		(NR_VECTORS + (8 * nr_cpu_ids)) :
+		(NR_VECTORS + (32 * nr_ioapics)));
+
+	if (nr < nr_irqs && nr > nr_irqs_gsi)
+		nr_irqs = nr;
+
+	return 0;
+}
+#endif
+
 /* --------------------------------------------------------------------------
                           ACPI-based IOAPIC Configuration
    -------------------------------------------------------------------------- */

include/linux/interrupt.h

@@ -467,6 +467,7 @@ int show_interrupts(struct seq_file *p, void *v);
 struct irq_desc;
 
 extern int early_irq_init(void);
+extern int arch_probe_nr_irqs(void);
 extern int arch_early_irq_init(void);
 extern int arch_init_chip_data(struct irq_desc *desc, int cpu);
 

kernel/irq/handle.c

@@ -59,10 +59,6 @@ EXPORT_SYMBOL_GPL(nr_irqs);
 
 #ifdef CONFIG_SPARSE_IRQ
 
-#ifndef max_nr_irqs
-#define max_nr_irqs(nr_cpus)	NR_IRQS
-#endif
-
 static struct irq_desc irq_desc_init = {
 	.irq	    = -1,
 	.status	    = IRQ_DISABLED,
@@ -137,9 +133,8 @@ 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);
-
+	 /* initialize nr_irqs based on nr_cpu_ids */
+	arch_probe_nr_irqs();
 	printk(KERN_INFO "NR_IRQS:%d nr_irqs:%d\n", NR_IRQS, nr_irqs);
 
 	desc = irq_desc_legacy;

kernel/softirq.c

@@ -795,6 +795,11 @@ int __init __weak early_irq_init(void)
 	return 0;
 }
 
+int __init __weak arch_probe_nr_irqs(void)
+{
+	return 0;
+}
+
 int __init __weak arch_early_irq_init(void)
 {
 	return 0;