[PATCH] x86: arch_probe_nr_irqs

[Yinghai Lu]

Impact: save RAM with large NR_CPUS, get smaller nr_irqs

Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>

---
 arch/x86/include/asm/irq_vectors.h |    7 ++-----
 arch/x86/kernel/io_apic.c          |   16 ++++++++++++++++
 include/linux/interrupt.h          |    1 +
 kernel/irq/handle.c                |    9 ++-------
 kernel/softirq.c                   |    5 +++++
 5 files changed, 26 insertions(+), 12 deletions(-)

Index: linux-2.6/arch/x86/include/asm/irq_vectors.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/irq_vectors.h
+++ linux-2.6/arch/x86/include/asm/irq_vectors.h
@@ -120,14 +120,11 @@
 # 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)
Index: linux-2.6/arch/x86/kernel/io_apic.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/io_apic.c
+++ linux-2.6/arch/x86/kernel/io_apic.c
@@ -3851,6 +3851,22 @@ 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
    -------------------------------------------------------------------------- */
Index: linux-2.6/include/linux/interrupt.h
===================================================================
--- linux-2.6.orig/include/linux/interrupt.h
+++ linux-2.6/include/linux/interrupt.h
@@ -481,6 +481,7 @@ int show_interrupts(struct seq_file *p,
 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);
 
Index: linux-2.6/kernel/irq/handle.c
===================================================================
--- linux-2.6.orig/kernel/irq/handle.c
+++ linux-2.6/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;
Index: linux-2.6/kernel/softirq.c
===================================================================
--- linux-2.6.orig/kernel/softirq.c
+++ linux-2.6/kernel/softirq.c
@@ -806,6 +806,11 @@ 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;
--
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