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>

23 files changed, 649 insertions, 163 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ac22bb7719f7..48ac688de3cd 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -238,6 +238,16 @@ config X86_HAS_BOOT_CPU_ID
         def_bool y
         depends on X86_VOYAGER
 
+config SPARSE_IRQ
+        bool "Support sparse irq numbering"
+        depends on PCI_MSI || HT_IRQ
+        default y
+        help
+          This enables support for sparse irq, esp for msi/msi-x. You may need
+          if you have lots of cards supports msi-x installed.
+
+          If you don't know what to do here, say Y.
+
 config X86_FIND_SMP_CONFIG
         def_bool y
         depends on X86_MPPARSE || X86_VOYAGER
diff --git a/arch/x86/include/asm/irq_vectors.h b/arch/x86/include/asm/irq_vectors.h
index 0005adb0f941..bb6b69a6b125 100644
--- a/arch/x86/include/asm/irq_vectors.h
+++ b/arch/x86/include/asm/irq_vectors.h
@@ -102,11 +102,20 @@
 #define invalid_vm86_irq(irq)   ((irq) < 3 || (irq) > 15)
 
 #if defined(CONFIG_X86_IO_APIC) && !defined(CONFIG_X86_VOYAGER)
+
+#ifndef CONFIG_SPARSE_IRQ
 # if NR_CPUS < MAX_IO_APICS
 #  define NR_IRQS (NR_VECTORS + (32 * NR_CPUS))
 # else
 #  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
+#endif
 
 #elif defined(CONFIG_X86_VOYAGER)
 
diff --git a/arch/x86/kernel/io_apic.c b/arch/x86/kernel/io_apic.c
index 9043251210fb..9de17f5c1125 100644
--- a/arch/x86/kernel/io_apic.c
+++ b/arch/x86/kernel/io_apic.c
@@ -108,8 +108,33 @@ static int __init parse_noapic(char *str)
 early_param("noapic", parse_noapic);
 
 struct irq_pin_list;
+
+/*
+ * This is performance-critical, we want to do it O(1)
+ *
+ * the indexing order of this array favors 1:1 mappings
+ * between pins and IRQs.
+ */
+
+struct irq_pin_list {
+        int apic, pin;
+        struct irq_pin_list *next;
+};
+
+static struct irq_pin_list *get_one_free_irq_2_pin(int cpu)
+{
+        struct irq_pin_list *pin;
+        int node;
+
+        node = cpu_to_node(cpu);
+
+        pin = kzalloc_node(sizeof(*pin), GFP_ATOMIC, node);
+        printk(KERN_DEBUG "  alloc irq_2_pin on cpu %d node %d\n", cpu, node);
+
+        return pin;
+}
+
 struct irq_cfg {
-        unsigned int irq;
         struct irq_pin_list *irq_2_pin;
         cpumask_t domain;
         cpumask_t old_domain;
@@ -119,83 +144,93 @@ struct irq_cfg {
 };
 
 /* irq_cfg is indexed by the sum of all RTEs in all I/O APICs. */
+#ifdef CONFIG_SPARSE_IRQ
+static struct irq_cfg irq_cfgx[] = {
+#else
 static struct irq_cfg irq_cfgx[NR_IRQS] = {
-        [0]  = { .irq =  0, .domain = CPU_MASK_ALL, .vector = IRQ0_VECTOR,  },
-        [1]  = { .irq =  1, .domain = CPU_MASK_ALL, .vector = IRQ1_VECTOR,  },
-        [2]  = { .irq =  2, .domain = CPU_MASK_ALL, .vector = IRQ2_VECTOR,  },
-        [3]  = { .irq =  3, .domain = CPU_MASK_ALL, .vector = IRQ3_VECTOR,  },
-        [4]  = { .irq =  4, .domain = CPU_MASK_ALL, .vector = IRQ4_VECTOR,  },
-        [5]  = { .irq =  5, .domain = CPU_MASK_ALL, .vector = IRQ5_VECTOR,  },
-        [6]  = { .irq =  6, .domain = CPU_MASK_ALL, .vector = IRQ6_VECTOR,  },
-        [7]  = { .irq =  7, .domain = CPU_MASK_ALL, .vector = IRQ7_VECTOR,  },
-        [8]  = { .irq =  8, .domain = CPU_MASK_ALL, .vector = IRQ8_VECTOR,  },
-        [9]  = { .irq =  9, .domain = CPU_MASK_ALL, .vector = IRQ9_VECTOR,  },
-        [10] = { .irq = 10, .domain = CPU_MASK_ALL, .vector = IRQ10_VECTOR, },
-        [11] = { .irq = 11, .domain = CPU_MASK_ALL, .vector = IRQ11_VECTOR, },
-        [12] = { .irq = 12, .domain = CPU_MASK_ALL, .vector = IRQ12_VECTOR, },
-        [13] = { .irq = 13, .domain = CPU_MASK_ALL, .vector = IRQ13_VECTOR, },
-        [14] = { .irq = 14, .domain = CPU_MASK_ALL, .vector = IRQ14_VECTOR, },
-        [15] = { .irq = 15, .domain = CPU_MASK_ALL, .vector = IRQ15_VECTOR, },
+#endif
+        [0]  = { .domain = CPU_MASK_ALL, .vector = IRQ0_VECTOR,  },
+        [1]  = { .domain = CPU_MASK_ALL, .vector = IRQ1_VECTOR,  },
+        [2]  = { .domain = CPU_MASK_ALL, .vector = IRQ2_VECTOR,  },
+        [3]  = { .domain = CPU_MASK_ALL, .vector = IRQ3_VECTOR,  },
+        [4]  = { .domain = CPU_MASK_ALL, .vector = IRQ4_VECTOR,  },
+        [5]  = { .domain = CPU_MASK_ALL, .vector = IRQ5_VECTOR,  },
+        [6]  = { .domain = CPU_MASK_ALL, .vector = IRQ6_VECTOR,  },
+        [7]  = { .domain = CPU_MASK_ALL, .vector = IRQ7_VECTOR,  },
+        [8]  = { .domain = CPU_MASK_ALL, .vector = IRQ8_VECTOR,  },
+        [9]  = { .domain = CPU_MASK_ALL, .vector = IRQ9_VECTOR,  },
+        [10] = { .domain = CPU_MASK_ALL, .vector = IRQ10_VECTOR, },
+        [11] = { .domain = CPU_MASK_ALL, .vector = IRQ11_VECTOR, },
+        [12] = { .domain = CPU_MASK_ALL, .vector = IRQ12_VECTOR, },
+        [13] = { .domain = CPU_MASK_ALL, .vector = IRQ13_VECTOR, },
+        [14] = { .domain = CPU_MASK_ALL, .vector = IRQ14_VECTOR, },
+        [15] = { .domain = CPU_MASK_ALL, .vector = IRQ15_VECTOR, },
 };
 
-#define for_each_irq_cfg(irq, cfg)              \
-        for (irq = 0, cfg = irq_cfgx; irq < nr_irqs; irq++, cfg++)
-
-static struct irq_cfg *irq_cfg(unsigned int irq)
+void __init arch_early_irq_init(void)
 {
-        return irq < nr_irqs ? irq_cfgx + irq : NULL;
-}
+        struct irq_cfg *cfg;
+        struct irq_desc *desc;
+        int count;
+        int i;
 
-static struct irq_cfg *irq_cfg_alloc(unsigned int irq)
-{
-        return irq_cfg(irq);
-}
+        cfg = irq_cfgx;
+        count = ARRAY_SIZE(irq_cfgx);
 
-/*
- * Rough estimation of how many shared IRQs there are, can be changed
- * anytime.
- */
-#define MAX_PLUS_SHARED_IRQS NR_IRQS
-#define PIN_MAP_SIZE (MAX_PLUS_SHARED_IRQS + NR_IRQS)
+        for (i = 0; i < count; i++) {
+                desc = irq_to_desc(i);
+                desc->chip_data = &cfg[i];
+        }
+}
 
-/*
- * This is performance-critical, we want to do it O(1)
- *
- * the indexing order of this array favors 1:1 mappings
- * between pins and IRQs.
- */
+#ifdef CONFIG_SPARSE_IRQ
+static struct irq_cfg *irq_cfg(unsigned int irq)
+{
+        struct irq_cfg *cfg = NULL;
+        struct irq_desc *desc;
 
-struct irq_pin_list {
-        int apic, pin;
-        struct irq_pin_list *next;
-};
+        desc = irq_to_desc(irq);
+        if (desc)
+                cfg = desc->chip_data;
 
-static struct irq_pin_list irq_2_pin_head[PIN_MAP_SIZE];
-static struct irq_pin_list *irq_2_pin_ptr;
+        return cfg;
+}
 
-static void __init irq_2_pin_init(void)
+static struct irq_cfg *get_one_free_irq_cfg(int cpu)
 {
-        struct irq_pin_list *pin = irq_2_pin_head;
-        int i;
+        struct irq_cfg *cfg;
+        int node;
+
+        node = cpu_to_node(cpu);
 
-        for (i = 1; i < PIN_MAP_SIZE; i++)
-                pin[i-1].next = &pin[i];
+        cfg = kzalloc_node(sizeof(*cfg), GFP_ATOMIC, node);
+        printk(KERN_DEBUG "  alloc irq_cfg on cpu %d node %d\n", cpu, node);
 
-        irq_2_pin_ptr = &pin[0];
+        return cfg;
 }
 
-static struct irq_pin_list *get_one_free_irq_2_pin(void)
+void arch_init_chip_data(struct irq_desc *desc, int cpu)
 {
-        struct irq_pin_list *pin = irq_2_pin_ptr;
+        struct irq_cfg *cfg;
 
-        if (!pin)
-                panic("can not get more irq_2_pin\n");
+        cfg = desc->chip_data;
+        if (!cfg) {
+                desc->chip_data = get_one_free_irq_cfg(cpu);
+                if (!desc->chip_data) {
+                        printk(KERN_ERR "can not alloc irq_cfg\n");
+                        BUG_ON(1);
+                }
+        }
+}
 
-        irq_2_pin_ptr = pin->next;
-        pin->next = NULL;
-        return pin;
+#else
+static struct irq_cfg *irq_cfg(unsigned int irq)
+{
+        return irq < nr_irqs ? irq_cfgx + irq : NULL;
 }
 
+#endif
+
 struct io_apic {
         unsigned int index;
         unsigned int unused[3];
@@ -397,16 +432,19 @@ static void set_ioapic_affinity_irq(unsigned int irq, cpumask_t mask)
  * shared ISA-space IRQs, so we have to support them. We are super
  * fast in the common case, and fast for shared ISA-space IRQs.
  */
-static void add_pin_to_irq(unsigned int irq, int apic, int pin)
+static void add_pin_to_irq_cpu(unsigned int irq, int cpu, int apic, int pin)
 {
-        struct irq_cfg *cfg;
         struct irq_pin_list *entry;
+        struct irq_cfg *cfg = irq_cfg(irq);
 
-        /* first time to refer irq_cfg, so with new */
-        cfg = irq_cfg_alloc(irq);
         entry = cfg->irq_2_pin;
         if (!entry) {
-                entry = get_one_free_irq_2_pin();
+                entry = get_one_free_irq_2_pin(cpu);
+                if (!entry) {
+                        printk(KERN_ERR "can not alloc irq_2_pin to add %d - %d\n",
+                                        apic, pin);
+                        return;
+                }
                 cfg->irq_2_pin = entry;
                 entry->apic = apic;
                 entry->pin = pin;
@@ -421,7 +459,7 @@ static void add_pin_to_irq(unsigned int irq, int apic, int pin)
                 entry = entry->next;
         }
 
-        entry->next = get_one_free_irq_2_pin();
+        entry->next = get_one_free_irq_2_pin(cpu);
         entry = entry->next;
         entry->apic = apic;
         entry->pin = pin;
@@ -430,7 +468,7 @@ static void add_pin_to_irq(unsigned int irq, int apic, int pin)
 /*
  * Reroute an IRQ to a different pin.
  */
-static void __init replace_pin_at_irq(unsigned int irq,
+static void __init replace_pin_at_irq(unsigned int irq, int cpu,
                                       int oldapic, int oldpin,
                                       int newapic, int newpin)
 {
@@ -451,7 +489,7 @@ static void __init replace_pin_at_irq(unsigned int irq,
 
         /* why? call replace before add? */
         if (!replaced)
-                add_pin_to_irq(irq, newapic, newpin);
+                add_pin_to_irq_cpu(irq, cpu, newapic, newpin);
 }
 
 static inline void io_apic_modify_irq(unsigned int irq,
@@ -1162,9 +1200,13 @@ void __setup_vector_irq(int cpu)
         /* This function must be called with vector_lock held */
         int irq, vector;
         struct irq_cfg *cfg;
+        struct irq_desc *desc;
 
         /* Mark the inuse vectors */
-        for_each_irq_cfg(irq, cfg) {
+        for_each_irq_desc(irq, desc) {
+                if (!desc)
+                        continue;
+                cfg = desc->chip_data;
                 if (!cpu_isset(cpu, cfg->domain))
                         continue;
                 vector = cfg->vector;
@@ -1356,6 +1398,8 @@ static void __init setup_IO_APIC_irqs(void)
 {
         int apic, pin, idx, irq;
         int notcon = 0;
+        struct irq_desc *desc;
+        int cpu = boot_cpu_id;
 
         apic_printk(APIC_VERBOSE, KERN_DEBUG "init IO_APIC IRQs\n");
 
@@ -1387,7 +1431,12 @@ static void __init setup_IO_APIC_irqs(void)
                         if (multi_timer_check(apic, irq))
                                 continue;
 #endif
-                        add_pin_to_irq(irq, apic, pin);
+                        desc = irq_to_desc_alloc_cpu(irq, cpu);
+                        if (!desc) {
+                                printk(KERN_INFO "can not get irq_desc for %d\n", irq);
+                                continue;
+                        }
+                        add_pin_to_irq_cpu(irq, cpu, apic, pin);
 
                         setup_IO_APIC_irq(apic, pin, irq,
                                         irq_trigger(idx), irq_polarity(idx));
@@ -1448,6 +1497,7 @@ __apicdebuginit(void) print_IO_APIC(void)
         union IO_APIC_reg_03 reg_03;
         unsigned long flags;
         struct irq_cfg *cfg;
+        struct irq_desc *desc;
         unsigned int irq;
 
         if (apic_verbosity == APIC_QUIET)
@@ -1537,8 +1587,13 @@ __apicdebuginit(void) print_IO_APIC(void)
         }
         }
         printk(KERN_DEBUG "IRQ to pin mappings:\n");
-        for_each_irq_cfg(irq, cfg) {
-                struct irq_pin_list *entry = cfg->irq_2_pin;
+        for_each_irq_desc(irq, desc) {
+                struct irq_pin_list *entry;
+
+                if (!desc)
+                        continue;
+                cfg = desc->chip_data;
+                entry = cfg->irq_2_pin;
                 if (!entry)
                         continue;
                 printk(KERN_DEBUG "IRQ%d ", irq);
@@ -2022,6 +2077,7 @@ static unsigned int startup_ioapic_irq(unsigned int irq)
 {
         int was_pending = 0;
         unsigned long flags;
+        struct irq_cfg *cfg;
 
         spin_lock_irqsave(&ioapic_lock, flags);
         if (irq < 16) {
@@ -2029,6 +2085,7 @@ static unsigned int startup_ioapic_irq(unsigned int irq)
                 if (i8259A_irq_pending(irq))
                         was_pending = 1;
         }
+        cfg = irq_cfg(irq);
         __unmask_IO_APIC_irq(irq);
         spin_unlock_irqrestore(&ioapic_lock, flags);
 
@@ -2178,6 +2235,9 @@ static void ir_irq_migration(struct work_struct *work)
         struct irq_desc *desc;
 
         for_each_irq_desc(irq, desc) {
+                if (!desc)
+                        continue;
+
                 if (desc->status & IRQ_MOVE_PENDING) {
                         unsigned long flags;
 
@@ -2229,6 +2289,9 @@ asmlinkage void smp_irq_move_cleanup_interrupt(void)
                 struct irq_cfg *cfg;
                 irq = __get_cpu_var(vector_irq)[vector];
 
+                if (irq == -1)
+                        continue;
+
                 desc = irq_to_desc(irq);
                 if (!desc)
                         continue;
@@ -2430,8 +2493,12 @@ static inline void init_IO_APIC_traps(void)
          * Also, we've got to be careful not to trash gate
          * 0x80, because int 0x80 is hm, kind of importantish. ;)
          */
-        for_each_irq_cfg(irq, cfg) {
-                if (IO_APIC_IRQ(irq) && !cfg->vector) {
+        for_each_irq_desc(irq, desc) {
+                if (!desc)
+                        continue;
+
+                cfg = desc->chip_data;
+                if (IO_APIC_IRQ(irq) && cfg && !cfg->vector) {
                         /*
                          * Hmm.. We don't have an entry for this,
                          * so default to an old-fashioned 8259
@@ -2439,11 +2506,9 @@ static inline void init_IO_APIC_traps(void)
                          */
                         if (irq < 16)
                                 make_8259A_irq(irq);
-                        else {
-                                desc = irq_to_desc(irq);
+                        else
                                 /* Strange. Oh, well.. */
                                 desc->chip = &no_irq_chip;
-                        }
                 }
         }
 }
@@ -2654,7 +2719,7 @@ static inline void __init check_timer(void)
                  * Ok, does IRQ0 through the IOAPIC work?
                  */
                 if (no_pin1) {
-                        add_pin_to_irq(0, apic1, pin1);
+                        add_pin_to_irq_cpu(0, boot_cpu_id, apic1, pin1);
                         setup_timer_IRQ0_pin(apic1, pin1, cfg->vector);
                 }
                 unmask_IO_APIC_irq(0);
@@ -2683,7 +2748,7 @@ static inline void __init check_timer(void)
                 /*
                  * legacy devices should be connected to IO APIC #0
                  */
-                replace_pin_at_irq(0, apic1, pin1, apic2, pin2);
+                replace_pin_at_irq(0, boot_cpu_id, apic1, pin1, apic2, pin2);
                 setup_timer_IRQ0_pin(apic2, pin2, cfg->vector);
                 unmask_IO_APIC_irq(0);
                 enable_8259A_irq(0);
@@ -2902,21 +2967,25 @@ unsigned int create_irq_nr(unsigned int irq_want)
         unsigned int irq;
         unsigned int new;
         unsigned long flags;
-        struct irq_cfg *cfg_new;
-
-        irq_want = nr_irqs - 1;
+        struct irq_cfg *cfg_new = NULL;
+        int cpu = boot_cpu_id;
+        struct irq_desc *desc_new = NULL;
 
         irq = 0;
         spin_lock_irqsave(&vector_lock, flags);
         for (new = irq_want; new > 0; new--) {
                 if (platform_legacy_irq(new))
                         continue;
-                cfg_new = irq_cfg(new);
-                if (cfg_new && cfg_new->vector != 0)
+
+                desc_new = irq_to_desc_alloc_cpu(new, cpu);
+                if (!desc_new) {
+                        printk(KERN_INFO "can not get irq_desc for %d\n", new);
+                        continue;
+                }
+                cfg_new = desc_new->chip_data;
+
+                if (cfg_new->vector != 0)
                         continue;
-                /* check if need to create one */
-                if (!cfg_new)
-                        cfg_new = irq_cfg_alloc(new);
                 if (__assign_irq_vector(new, TARGET_CPUS) == 0)
                         irq = new;
                 break;
@@ -2925,6 +2994,9 @@ unsigned int create_irq_nr(unsigned int irq_want)
 
         if (irq > 0) {
                 dynamic_irq_init(irq);
+                /* restore it, in case dynamic_irq_init clear it */
+                if (desc_new)
+                        desc_new->chip_data = cfg_new;
         }
         return irq;
 }
@@ -2944,8 +3016,16 @@ int create_irq(void)
 void destroy_irq(unsigned int irq)
 {
         unsigned long flags;
+        struct irq_cfg *cfg;
+        struct irq_desc *desc;
 
+        /* store it, in case dynamic_irq_cleanup clear it */
+        desc = irq_to_desc(irq);
+        cfg = desc->chip_data;
         dynamic_irq_cleanup(irq);
+        /* connect back irq_cfg */
+        if (desc)
+                desc->chip_data = cfg;
 
 #ifdef CONFIG_INTR_REMAP
         free_irte(irq);
@@ -3195,26 +3275,13 @@ static int setup_msi_irq(struct pci_dev *dev, struct msi_desc *desc, int irq)
         return 0;
 }
 
-static unsigned int build_irq_for_pci_dev(struct pci_dev *dev)
-{
-        unsigned int irq;
-
-        irq = dev->bus->number;
-        irq <<= 8;
-        irq |= dev->devfn;
-        irq <<= 12;
-
-        return irq;
-}
-
-int arch_setup_msi_irq(struct pci_dev *dev, struct msi_desc *desc)
+int arch_setup_msi_irq(struct pci_dev *dev, struct msi_desc *msidesc)
 {
         unsigned int irq;
         int ret;
         unsigned int irq_want;
 
-        irq_want = build_irq_for_pci_dev(dev) + 0x100;
-
+        irq_want = nr_irqs - 1;
         irq = create_irq_nr(irq_want);
         if (irq == 0)
                 return -1;
@@ -3228,7 +3295,7 @@ int arch_setup_msi_irq(struct pci_dev *dev, struct msi_desc *desc)
                 goto error;
 no_ir:
 #endif
-        ret = setup_msi_irq(dev, desc, irq);
+        ret = setup_msi_irq(dev, msidesc, irq);
         if (ret < 0) {
                 destroy_irq(irq);
                 return ret;
@@ -3246,7 +3313,7 @@ int arch_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
 {
         unsigned int irq;
         int ret, sub_handle;
-        struct msi_desc *desc;
+        struct msi_desc *msidesc;
         unsigned int irq_want;
 
 #ifdef CONFIG_INTR_REMAP
@@ -3254,10 +3321,11 @@ int arch_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
         int index = 0;
 #endif
 
-        irq_want = build_irq_for_pci_dev(dev) + 0x100;
+        irq_want = nr_irqs - 1;
         sub_handle = 0;
-        list_for_each_entry(desc, &dev->msi_list, list) {
-                irq = create_irq_nr(irq_want--);
+        list_for_each_entry(msidesc, &dev->msi_list, list) {
+                irq = create_irq_nr(irq_want);
+                irq_want--;
                 if (irq == 0)
                         return -1;
 #ifdef CONFIG_INTR_REMAP
@@ -3289,7 +3357,7 @@ int arch_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
                 }
 no_ir:
 #endif
-                ret = setup_msi_irq(dev, desc, irq);
+                ret = setup_msi_irq(dev, msidesc, irq);
                 if (ret < 0)
                         goto error;
                 sub_handle++;
@@ -3707,17 +3775,29 @@ int __init io_apic_get_version(int ioapic)
 
 int io_apic_set_pci_routing (int ioapic, int pin, int irq, int triggering, int polarity)
 {
+        struct irq_desc *desc;
+        struct irq_cfg *cfg;
+        int cpu = boot_cpu_id;
+
         if (!IO_APIC_IRQ(irq)) {
                 apic_printk(APIC_QUIET,KERN_ERR "IOAPIC[%d]: Invalid reference to IRQ 0\n",
                         ioapic);
                 return -EINVAL;
         }
 
+        desc = irq_to_desc_alloc_cpu(irq, cpu);
+        if (!desc) {
+                printk(KERN_INFO "can not get irq_desc %d\n", irq);
+                return 0;
+        }
+
         /*
          * IRQs < 16 are already in the irq_2_pin[] map
          */
-        if (irq >= 16)
-                add_pin_to_irq(irq, ioapic, pin);
+        if (irq >= 16) {
+                cfg = desc->chip_data;
+                add_pin_to_irq_cpu(irq, cpu, ioapic, pin);
+        }
 
         setup_IO_APIC_irq(ioapic, pin, irq, triggering, polarity);
 
@@ -3773,7 +3853,8 @@ void __init setup_ioapic_dest(void)
                          * when you have too many devices, because at that time only boot
                          * cpu is online.
                          */
-                        cfg = irq_cfg(irq);
+                        desc = irq_to_desc(irq);
+                        cfg = desc->chip_data;
                         if (!cfg->vector) {
                                 setup_IO_APIC_irq(ioapic, pin, irq,
                                                   irq_trigger(irq_entry),
@@ -3785,7 +3866,6 @@ void __init setup_ioapic_dest(void)
                         /*
                          * Honour affinities which have been set in early boot
                          */
-                        desc = irq_to_desc(irq);
                         if (desc->status &
                             (IRQ_NO_BALANCING | IRQ_AFFINITY_SET))
                                 mask = desc->affinity;
@@ -3846,7 +3926,6 @@ void __init ioapic_init_mappings(void)
         struct resource *ioapic_res;
         int i;
 
-        irq_2_pin_init();
         ioapic_res = ioapic_setup_resources();
         for (i = 0; i < nr_ioapics; i++) {
                 if (smp_found_config) {
diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index d1d4dc52f649..3f1d9d18df67 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -118,6 +118,9 @@ int show_interrupts(struct seq_file *p, void *v)
         }
 
         desc = irq_to_desc(i);
+        if (!desc)
+                return 0;
+
         spin_lock_irqsave(&desc->lock, flags);
 #ifndef CONFIG_SMP
         any_count = kstat_irqs(i);
diff --git a/arch/x86/kernel/irq_32.c b/arch/x86/kernel/irq_32.c
index a51382672de0..119fc9c8ff7f 100644
--- a/arch/x86/kernel/irq_32.c
+++ b/arch/x86/kernel/irq_32.c
@@ -242,6 +242,8 @@ void fixup_irqs(cpumask_t map)
         for_each_irq_desc(irq, desc) {
                 cpumask_t mask;
 
+                if (!desc)
+                        continue;
                 if (irq == 2)
                         continue;
 
diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
index 60eb84eb77a0..900009c70591 100644
--- a/arch/x86/kernel/irq_64.c
+++ b/arch/x86/kernel/irq_64.c
@@ -94,6 +94,8 @@ void fixup_irqs(cpumask_t map)
                 int break_affinity = 0;
                 int set_affinity = 1;
 
+                if (!desc)
+                        continue;
                 if (irq == 2)
                         continue;
 
diff --git a/arch/x86/kernel/irqinit_32.c b/arch/x86/kernel/irqinit_32.c
index 845aa9803e80..5a5651b7f9e6 100644
--- a/arch/x86/kernel/irqinit_32.c
+++ b/arch/x86/kernel/irqinit_32.c
@@ -69,7 +69,6 @@ void __init init_ISA_irqs (void)
          * 16 old-style INTA-cycle interrupts:
          */
         for (i = 0; i < 16; i++) {
-                /* first time call this irq_desc */
                 struct irq_desc *desc = irq_to_desc(i);
 
                 desc->status = IRQ_DISABLED;
diff --git a/arch/x86/kernel/irqinit_64.c b/arch/x86/kernel/irqinit_64.c
index ff0235391285..cd9f42d028d9 100644
--- a/arch/x86/kernel/irqinit_64.c
+++ b/arch/x86/kernel/irqinit_64.c
@@ -143,7 +143,6 @@ void __init init_ISA_irqs(void)
         init_8259A(0);
 
         for (i = 0; i < 16; i++) {
-                /* first time call this irq_desc */
                 struct irq_desc *desc = irq_to_desc(i);
 
                 desc->status = IRQ_DISABLED;
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 675076f5fca8..d26891bfcd41 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -558,23 +558,9 @@ struct timer_rand_state {
         unsigned dont_count_entropy:1;
 };
 
-static struct timer_rand_state *irq_timer_state[NR_IRQS];
-
-static struct timer_rand_state *get_timer_rand_state(unsigned int irq)
-{
-        if (irq >= nr_irqs)
-                return NULL;
-
-        return irq_timer_state[irq];
-}
-
-static void set_timer_rand_state(unsigned int irq, struct timer_rand_state *state)
-{
-        if (irq >= nr_irqs)
-                return;
-
-        irq_timer_state[irq] = state;
-}
+#ifndef CONFIG_SPARSE_IRQ
+struct timer_rand_state *irq_timer_state[NR_IRQS];
+#endif
 
 static struct timer_rand_state input_timer_state;
 
@@ -933,8 +919,10 @@ void rand_initialize_irq(int irq)
 {
         struct timer_rand_state *state;
 
+#ifndef CONFIG_SPARSE_IRQ
         if (irq >= nr_irqs)
                 return;
+#endif
 
         state = get_timer_rand_state(irq);
 
diff --git a/drivers/pci/intr_remapping.c b/drivers/pci/intr_remapping.c
index 2de5a3238c94..c9958ec5e25e 100644
--- a/drivers/pci/intr_remapping.c
+++ b/drivers/pci/intr_remapping.c
@@ -19,17 +19,75 @@ struct irq_2_iommu {
         u8  irte_mask;
 };
 
-static struct irq_2_iommu irq_2_iommuX[NR_IRQS];
+#ifdef CONFIG_SPARSE_IRQ
+static struct irq_2_iommu *get_one_free_irq_2_iommu(int cpu)
+{
+        struct irq_2_iommu *iommu;
+        int node;
+
+        node = cpu_to_node(cpu);
+
+        iommu = kzalloc_node(sizeof(*iommu), GFP_ATOMIC, node);
+        printk(KERN_DEBUG "alloc irq_2_iommu on cpu %d node %d\n", cpu, node);
+
+        return iommu;
+}
 
 static struct irq_2_iommu *irq_2_iommu(unsigned int irq)
 {
-        return (irq < nr_irqs) ? irq_2_iommuX + irq : NULL;
+        struct irq_desc *desc;
+
+        desc = irq_to_desc(irq);
+
+        if (WARN_ON_ONCE(!desc))
+                return NULL;
+
+        return desc->irq_2_iommu;
+}
+
+static struct irq_2_iommu *irq_2_iommu_alloc_cpu(unsigned int irq, int cpu)
+{
+        struct irq_desc *desc;
+        struct irq_2_iommu *irq_iommu;
+
+        /*
+         * alloc irq desc if not allocated already.
+         */
+        desc = irq_to_desc_alloc_cpu(irq, cpu);
+        if (!desc) {
+                printk(KERN_INFO "can not get irq_desc for %d\n", irq);
+                return NULL;
+        }
+
+        irq_iommu = desc->irq_2_iommu;
+
+        if (!irq_iommu)
+                desc->irq_2_iommu = get_one_free_irq_2_iommu(cpu);
+
+        return desc->irq_2_iommu;
 }
 
 static struct irq_2_iommu *irq_2_iommu_alloc(unsigned int irq)
 {
+        return irq_2_iommu_alloc_cpu(irq, boot_cpu_id);
+}
+
+#else /* !CONFIG_SPARSE_IRQ */
+
+static struct irq_2_iommu irq_2_iommuX[NR_IRQS];
+
+static struct irq_2_iommu *irq_2_iommu(unsigned int irq)
+{
+        if (irq < nr_irqs)
+                return &irq_2_iommuX[irq];
+
+        return NULL;
+}
+static struct irq_2_iommu *irq_2_iommu_alloc(unsigned int irq)
+{
         return irq_2_iommu(irq);
 }
+#endif
 
 static DEFINE_SPINLOCK(irq_2_ir_lock);
 
@@ -86,9 +144,11 @@ int alloc_irte(struct intel_iommu *iommu, int irq, u16 count)
         if (!count)
                 return -1;
 
+#ifndef CONFIG_SPARSE_IRQ
         /* protect irq_2_iommu_alloc later */
         if (irq >= nr_irqs)
                 return -1;
+#endif
 
         /*
          * start the IRTE search from index 0.
@@ -130,6 +190,12 @@ int alloc_irte(struct intel_iommu *iommu, int irq, u16 count)
                 table->base[i].present = 1;
 
         irq_iommu = irq_2_iommu_alloc(irq);
+        if (!irq_iommu) {
+                spin_unlock(&irq_2_ir_lock);
+                printk(KERN_ERR "can't allocate irq_2_iommu\n");
+                return -1;
+        }
+
         irq_iommu->iommu = iommu;
         irq_iommu->irte_index =  index;
         irq_iommu->sub_handle = 0;
@@ -177,6 +243,12 @@ int set_irte_irq(int irq, struct intel_iommu *iommu, u16 index, u16 subhandle)
 
         irq_iommu = irq_2_iommu_alloc(irq);
 
+        if (!irq_iommu) {
+                spin_unlock(&irq_2_ir_lock);
+                printk(KERN_ERR "can't allocate irq_2_iommu\n");
+                return -1;
+        }
+
         irq_iommu->iommu = iommu;
         irq_iommu->irte_index = index;
         irq_iommu->sub_handle = subhandle;
diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 1e3b934a4cf7..2924faa7f6c4 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -141,8 +141,12 @@ static void init_evtchn_cpu_bindings(void)
         int i;
 
         /* By default all event channels notify CPU#0. */
-        for_each_irq_desc(i, desc)
+        for_each_irq_desc(i, desc) {
+                if (!desc)
+                        continue;
+
                 desc->affinity = cpumask_of_cpu(0);
+        }
 #endif
 
         memset(cpu_evtchn, 0, sizeof(cpu_evtchn));
@@ -231,7 +235,7 @@ static int find_unbound_irq(void)
         int irq;
 
         /* Only allocate from dynirq range */
-        for_each_irq_nr(irq)
+        for (irq = 0; irq < nr_irqs; irq++)
                 if (irq_bindcount[irq] == 0)
                         break;
 
@@ -792,7 +796,7 @@ void xen_irq_resume(void)
                 mask_evtchn(evtchn);
 
         /* No IRQ <-> event-channel mappings. */
-        for_each_irq_nr(irq)
+        for (irq = 0; irq < nr_irqs; irq++)
                 irq_info[irq].evtchn = 0; /* zap event-channel binding */
 
         for (evtchn = 0; evtchn < NR_EVENT_CHANNELS; evtchn++)
@@ -824,7 +828,7 @@ void __init xen_init_IRQ(void)
                 mask_evtchn(i);
 
         /* Dynamic IRQ space is currently unbound. Zero the refcnts. */
-        for_each_irq_nr(i)
+        for (i = 0; i < nr_irqs; i++)
                 irq_bindcount[i] = 0;
 
         irq_ctx_init(smp_processor_id());
diff --git a/fs/proc/stat.c b/fs/proc/stat.c
index 81904f07679d..a13431ab7c65 100644
--- a/fs/proc/stat.c
+++ b/fs/proc/stat.c
@@ -27,6 +27,7 @@ static int show_stat(struct seq_file *p, void *v)
         u64 sum = 0;
         struct timespec boottime;
         unsigned int per_irq_sum;
+        struct irq_desc *desc;
 
         user = nice = system = idle = iowait =
                 irq = softirq = steal = cputime64_zero;
@@ -44,10 +45,11 @@ static int show_stat(struct seq_file *p, void *v)
                 softirq = cputime64_add(softirq, kstat_cpu(i).cpustat.softirq);
                 steal = cputime64_add(steal, kstat_cpu(i).cpustat.steal);
                 guest = cputime64_add(guest, kstat_cpu(i).cpustat.guest);
-
-                for_each_irq_nr(j)
+                for_each_irq_desc(j, desc) {
+                        if (!desc)
+                                continue;
                         sum += kstat_irqs_cpu(j, i);
-
+                }
                 sum += arch_irq_stat_cpu(i);
         }
         sum += arch_irq_stat();
@@ -90,11 +92,14 @@ static int show_stat(struct seq_file *p, void *v)
         seq_printf(p, "intr %llu", (unsigned long long)sum);
 
         /* sum again ? it could be updated? */
-        for_each_irq_nr(j) {
+        for (j = 0; j < NR_IRQS; j++) {
+                desc = irq_to_desc(j);
                 per_irq_sum = 0;
 
-                for_each_possible_cpu(i)
-                        per_irq_sum += kstat_irqs_cpu(j, i);
+                if (desc) {
+                        for_each_possible_cpu(i)
+                                per_irq_sum += kstat_irqs_cpu(j, i);
+                }
 
                 seq_printf(p, " %u", per_irq_sum);
         }
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index f58a0cf8929a..79e915e7e8a5 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -18,6 +18,8 @@
 #include <asm/ptrace.h>
 #include <asm/system.h>
 
+extern int nr_irqs;
+
 /*
  * These correspond to the IORESOURCE_IRQ_* defines in
  * linux/ioport.h to select the interrupt line behaviour.  When
diff --git a/include/linux/irq.h b/include/linux/irq.h
index 3dddfa703ebd..63b00439d4d2 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -129,6 +129,8 @@ struct irq_chip {
         const char      *typename;
 };
 
+struct timer_rand_state;
+struct irq_2_iommu;
 /**
  * struct irq_desc - interrupt descriptor
  * @irq:                interrupt number for this descriptor
@@ -154,6 +156,13 @@ struct irq_chip {
  */
 struct irq_desc {
         unsigned int            irq;
+#ifdef CONFIG_SPARSE_IRQ
+        struct timer_rand_state *timer_rand_state;
+        unsigned int            *kstat_irqs;
+# ifdef CONFIG_INTR_REMAP
+        struct irq_2_iommu      *irq_2_iommu;
+# endif
+#endif
         irq_flow_handler_t      handle_irq;
         struct irq_chip         *chip;
         struct msi_desc         *msi_desc;
@@ -181,14 +190,52 @@ struct irq_desc {
         const char              *name;
 } ____cacheline_internodealigned_in_smp;
 
+extern void early_irq_init(void);
+extern void arch_early_irq_init(void);
+extern void arch_init_chip_data(struct irq_desc *desc, int cpu);
+extern void arch_init_copy_chip_data(struct irq_desc *old_desc,
+                                        struct irq_desc *desc, int cpu);
+extern void arch_free_chip_data(struct irq_desc *old_desc, struct irq_desc *desc);
+
+#ifndef CONFIG_SPARSE_IRQ
 
 extern struct irq_desc irq_desc[NR_IRQS];
 
 static inline struct irq_desc *irq_to_desc(unsigned int irq)
 {
-        return (irq < nr_irqs) ? irq_desc + irq : NULL;
+        return (irq < NR_IRQS) ? irq_desc + irq : NULL;
+}
+static inline struct irq_desc *irq_to_desc_alloc_cpu(unsigned int irq, int cpu)
+{
+        return irq_to_desc(irq);
 }
 
+#ifdef CONFIG_GENERIC_HARDIRQS
+# define for_each_irq_desc(irq, desc)           \
+        for (irq = 0, desc = irq_desc; irq < nr_irqs; irq++, desc++)
+# define for_each_irq_desc_reverse(irq, desc)                          \
+        for (irq = nr_irqs - 1, desc = irq_desc + (nr_irqs - 1);        \
+            irq >= 0; irq--, desc--)
+#endif
+
+#else
+
+extern struct irq_desc *irq_to_desc(unsigned int irq);
+extern struct irq_desc *irq_to_desc_alloc_cpu(unsigned int irq, int cpu);
+extern struct irq_desc *move_irq_desc(struct irq_desc *old_desc, int cpu);
+
+# define for_each_irq_desc(irq, desc)           \
+        for (irq = 0, desc = irq_to_desc(irq); irq < nr_irqs; irq++, desc = irq_to_desc(irq))
+# define for_each_irq_desc_reverse(irq, desc)                          \
+        for (irq = nr_irqs - 1, desc = irq_to_desc(irq); irq >= 0; irq--, desc = irq_to_desc(irq))
+
+#define kstat_irqs_this_cpu(DESC) \
+        ((DESC)->kstat_irqs[smp_processor_id()])
+#define kstat_incr_irqs_this_cpu(irqno, DESC) \
+        ((DESC)->kstat_irqs[smp_processor_id()]++)
+
+#endif
+
 /*
  * Migration helpers for obsolete names, they will go away:
  */
@@ -380,6 +427,11 @@ extern int set_irq_msi(unsigned int irq, struct msi_desc *entry);
 #define get_irq_data(irq)       (irq_to_desc(irq)->handler_data)
 #define get_irq_msi(irq)        (irq_to_desc(irq)->msi_desc)
 
+#define get_irq_desc_chip(desc)         ((desc)->chip)
+#define get_irq_desc_chip_data(desc)    ((desc)->chip_data)
+#define get_irq_desc_data(desc)         ((desc)->handler_data)
+#define get_irq_desc_msi(desc)          ((desc)->msi_desc)
+
 #endif /* CONFIG_GENERIC_HARDIRQS */
 
 #endif /* !CONFIG_S390 */
diff --git a/include/linux/irqnr.h b/include/linux/irqnr.h
index 452c280c8115..7a299e989f8b 100644
--- a/include/linux/irqnr.h
+++ b/include/linux/irqnr.h
@@ -7,18 +7,10 @@
 
 # define for_each_irq_desc(irq, desc)           \
         for (irq = 0; irq < nr_irqs; irq++)
-#else
-extern int nr_irqs;
 
-# define for_each_irq_desc(irq, desc)           \
-        for (irq = 0, desc = irq_desc; irq < nr_irqs; irq++, desc++)
-
-# define for_each_irq_desc_reverse(irq, desc)                           \
-        for (irq = nr_irqs - 1, desc = irq_desc + (nr_irqs - 1);        \
-             irq >= 0; irq--, desc--)
+static inline early_sparse_irq_init(void)
+{
+}
 #endif
 
-#define for_each_irq_nr(irq)                    \
-        for (irq = 0; irq < nr_irqs; irq++)
-
 #endif
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
diff --git a/include/linux/random.h b/include/linux/random.h
index 36f125c0c603..ad9daa2374d5 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -44,6 +44,57 @@ struct rand_pool_info {
 
 extern void rand_initialize_irq(int irq);
 
+struct timer_rand_state;
+#ifndef CONFIG_SPARSE_IRQ
+
+extern struct timer_rand_state *irq_timer_state[];
+
+extern int nr_irqs;
+static inline struct timer_rand_state *get_timer_rand_state(unsigned int irq)
+{
+        if (irq >= nr_irqs)
+                return NULL;
+
+        return irq_timer_state[irq];
+}
+
+static inline void set_timer_rand_state(unsigned int irq, struct timer_rand_state *state)
+{
+        if (irq >= nr_irqs)
+                return;
+
+        irq_timer_state[irq] = state;
+}
+
+#else
+
+#include <linux/irq.h>
+static inline struct timer_rand_state *get_timer_rand_state(unsigned int irq)
+{
+        struct irq_desc *desc;
+
+        desc = irq_to_desc(irq);
+
+        if (!desc)
+                return NULL;
+
+        return desc->timer_rand_state;
+}
+
+static inline void set_timer_rand_state(unsigned int irq, struct timer_rand_state *state)
+{
+        struct irq_desc *desc;
+
+        desc = irq_to_desc(irq);
+
+        if (!desc)
+                return;
+
+        desc->timer_rand_state = state;
+}
+#endif
+
+
 extern void add_input_randomness(unsigned int type, unsigned int code,
                                  unsigned int value);
 extern void add_interrupt_randomness(int irq);
diff --git a/init/main.c b/init/main.c
index 7e117a231af1..c1f999a3cf31 100644
--- a/init/main.c
+++ b/init/main.c
@@ -539,6 +539,15 @@ void __init __weak thread_info_cache_init(void)
 {
 }
 
+void __init __weak arch_early_irq_init(void)
+{
+}
+
+void __init __weak early_irq_init(void)
+{
+        arch_early_irq_init();
+}
+
 asmlinkage void __init start_kernel(void)
 {
         char * command_line;
@@ -603,6 +612,8 @@ asmlinkage void __init start_kernel(void)
         sort_main_extable();
         trap_init();
         rcu_init();
+        /* init some links before init_ISA_irqs() */
+        early_irq_init();
         init_IRQ();
         pidhash_init();
         init_timers();
diff --git a/kernel/irq/autoprobe.c b/kernel/irq/autoprobe.c
index cc0f7321b8ce..650ce4102a63 100644
--- a/kernel/irq/autoprobe.c
+++ b/kernel/irq/autoprobe.c
@@ -40,6 +40,9 @@ unsigned long probe_irq_on(void)
          * flush such a longstanding irq before considering it as spurious.
          */
         for_each_irq_desc_reverse(i, desc) {
+                if (!desc)
+                        continue;
+
                 spin_lock_irq(&desc->lock);
                 if (!desc->action && !(desc->status & IRQ_NOPROBE)) {
                         /*
@@ -68,6 +71,9 @@ unsigned long probe_irq_on(void)
          * happened in the previous stage, it may have masked itself)
          */
         for_each_irq_desc_reverse(i, desc) {
+                if (!desc)
+                        continue;
+
                 spin_lock_irq(&desc->lock);
                 if (!desc->action && !(desc->status & IRQ_NOPROBE)) {
                         desc->status |= IRQ_AUTODETECT | IRQ_WAITING;
@@ -86,6 +92,9 @@ unsigned long probe_irq_on(void)
          * Now filter out any obviously spurious interrupts
          */
         for_each_irq_desc(i, desc) {
+                if (!desc)
+                        continue;
+
                 spin_lock_irq(&desc->lock);
                 status = desc->status;
 
@@ -124,6 +133,9 @@ unsigned int probe_irq_mask(unsigned long val)
         int i;
 
         for_each_irq_desc(i, desc) {
+                if (!desc)
+                        continue;
+
                 spin_lock_irq(&desc->lock);
                 status = desc->status;
 
@@ -166,6 +178,9 @@ int probe_irq_off(unsigned long val)
         unsigned int status;
 
         for_each_irq_desc(i, desc) {
+                if (!desc)
+                        continue;
+
                 spin_lock_irq(&desc->lock);
                 status = desc->status;
 
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index 10b5092e9bfe..8e4fce4a1b1f 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -24,9 +24,10 @@
  */
 void dynamic_irq_init(unsigned int irq)
 {
-        struct irq_desc *desc = irq_to_desc(irq);
+        struct irq_desc *desc;
         unsigned long flags;
 
+        desc = irq_to_desc(irq);
         if (!desc) {
                 WARN(1, KERN_ERR "Trying to initialize invalid IRQ%d\n", irq);
                 return;
diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index c815b42d0f5b..96ca203eb51b 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -15,9 +15,16 @@
 #include <linux/random.h>
 #include <linux/interrupt.h>
 #include <linux/kernel_stat.h>
+#include <linux/rculist.h>
+#include <linux/hash.h>
 
 #include "internals.h"
 
+/*
+ * lockdep: we want to handle all irq_desc locks as a single lock-class:
+ */
+static struct lock_class_key irq_desc_lock_class;
+
 /**
  * handle_bad_irq - handle spurious and unhandled irqs
  * @irq:       the interrupt number
@@ -49,6 +56,155 @@ void handle_bad_irq(unsigned int irq, struct irq_desc *desc)
 int nr_irqs = NR_IRQS;
 EXPORT_SYMBOL_GPL(nr_irqs);
 
+void __init __attribute__((weak)) arch_early_irq_init(void)
+{
+}
+
+#ifdef CONFIG_SPARSE_IRQ
+static struct irq_desc irq_desc_init = {
+        .irq        = -1,
+        .status     = IRQ_DISABLED,
+        .chip       = &no_irq_chip,
+        .handle_irq = handle_bad_irq,
+        .depth      = 1,
+        .lock       = __SPIN_LOCK_UNLOCKED(irq_desc_init.lock),
+#ifdef CONFIG_SMP
+        .affinity   = CPU_MASK_ALL
+#endif
+};
+
+static void init_kstat_irqs(struct irq_desc *desc, int cpu, int nr)
+{
+        unsigned long bytes;
+        char *ptr;
+        int node;
+
+        /* Compute how many bytes we need per irq and allocate them */
+        bytes = nr * sizeof(unsigned int);
+
+        node = cpu_to_node(cpu);
+        ptr = kzalloc_node(bytes, GFP_ATOMIC, node);
+        printk(KERN_DEBUG "  alloc kstat_irqs on cpu %d node %d\n", cpu, node);
+
+        if (ptr)
+                desc->kstat_irqs = (unsigned int *)ptr;
+}
+
+void __attribute__((weak)) arch_init_chip_data(struct irq_desc *desc, int cpu)
+{
+}
+
+static void init_one_irq_desc(int irq, struct irq_desc *desc, int cpu)
+{
+        memcpy(desc, &irq_desc_init, sizeof(struct irq_desc));
+        desc->irq = irq;
+#ifdef CONFIG_SMP
+        desc->cpu = cpu;
+#endif
+        lockdep_set_class(&desc->lock, &irq_desc_lock_class);
+        init_kstat_irqs(desc, cpu, nr_cpu_ids);
+        if (!desc->kstat_irqs) {
+                printk(KERN_ERR "can not alloc kstat_irqs\n");
+                BUG_ON(1);
+        }
+        arch_init_chip_data(desc, cpu);
+}
+
+/*
+ * Protect the sparse_irqs:
+ */
+static DEFINE_SPINLOCK(sparse_irq_lock);
+
+struct irq_desc *irq_desc_ptrs[NR_IRQS] __read_mostly;
+
+static struct irq_desc irq_desc_legacy[16] __cacheline_aligned_in_smp = {
+        [0 ... 15] = {
+                .irq        = -1,
+                .status     = IRQ_DISABLED,
+                .chip       = &no_irq_chip,
+                .handle_irq = handle_bad_irq,
+                .depth      = 1,
+                .lock       = __SPIN_LOCK_UNLOCKED(irq_desc_init.lock),
+#ifdef CONFIG_SMP
+                .affinity   = CPU_MASK_ALL
+#endif
+        }
+};
+
+/* FIXME: use bootmem alloc ...*/
+static unsigned int kstat_irqs_legacy[16][NR_CPUS];
+
+void __init early_irq_init(void)
+{
+        struct irq_desc *desc;
+        int legacy_count;
+        int i;
+
+        desc = irq_desc_legacy;
+        legacy_count = ARRAY_SIZE(irq_desc_legacy);
+
+        for (i = 0; i < legacy_count; i++) {
+                desc[i].irq = i;
+                desc[i].kstat_irqs = kstat_irqs_legacy[i];
+
+                irq_desc_ptrs[i] = desc + i;
+        }
+
+        for (i = legacy_count; i < NR_IRQS; i++)
+                irq_desc_ptrs[i] = NULL;
+
+        arch_early_irq_init();
+}
+
+struct irq_desc *irq_to_desc(unsigned int irq)
+{
+        return (irq < NR_IRQS) ? irq_desc_ptrs[irq] : NULL;
+}
+
+struct irq_desc *irq_to_desc_alloc_cpu(unsigned int irq, int cpu)
+{
+        struct irq_desc *desc;
+        unsigned long flags;
+        int node;
+
+        if (irq >= NR_IRQS) {
+                printk(KERN_WARNING "irq >= NR_IRQS in irq_to_desc_alloc: %d %d\n",
+                                irq, NR_IRQS);
+                WARN_ON(1);
+                return NULL;
+        }
+
+        desc = irq_desc_ptrs[irq];
+        if (desc)
+                return desc;
+
+        spin_lock_irqsave(&sparse_irq_lock, flags);
+
+        /* We have to check it to avoid races with another CPU */
+        desc = irq_desc_ptrs[irq];
+        if (desc)
+                goto out_unlock;
+
+        node = cpu_to_node(cpu);
+        desc = kzalloc_node(sizeof(*desc), GFP_ATOMIC, node);
+        printk(KERN_DEBUG "  alloc irq_desc for %d on cpu %d node %d\n",
+                 irq, cpu, node);
+        if (!desc) {
+                printk(KERN_ERR "can not alloc irq_desc\n");
+                BUG_ON(1);
+        }
+        init_one_irq_desc(irq, desc, cpu);
+
+        irq_desc_ptrs[irq] = desc;
+
+out_unlock:
+        spin_unlock_irqrestore(&sparse_irq_lock, flags);
+
+        return desc;
+}
+
+#else
+
 struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
         [0 ... NR_IRQS-1] = {
                 .status = IRQ_DISABLED,
@@ -62,6 +218,8 @@ struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
         }
 };
 
+#endif
+
 /*
  * What should we do if we get a hw irq event on an illegal vector?
  * Each architecture has to answer this themself.
@@ -261,17 +419,28 @@ out:
 
 
 #ifdef CONFIG_TRACE_IRQFLAGS
-/*
- * lockdep: we want to handle all irq_desc locks as a single lock-class:
- */
-static struct lock_class_key irq_desc_lock_class;
-
 void early_init_irq_lock_class(void)
 {
+#ifndef CONFIG_SPARSE_IRQ
         struct irq_desc *desc;
         int i;
 
-        for_each_irq_desc(i, desc)
+        for_each_irq_desc(i, desc) {
+                if (!desc)
+                        continue;
+
                 lockdep_set_class(&desc->lock, &irq_desc_lock_class);
+        }
+#endif
+}
+#endif
+
+#ifdef CONFIG_SPARSE_IRQ
+unsigned int kstat_irqs_cpu(unsigned int irq, int cpu)
+{
+        struct irq_desc *desc = irq_to_desc(irq);
+        return desc->kstat_irqs[cpu];
 }
 #endif
+EXPORT_SYMBOL(kstat_irqs_cpu);
+
diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index d257e7d6a8a4..f6b3440f05bc 100644
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -243,7 +243,11 @@ void init_irq_proc(void)
         /*
          * Create entries for all existing IRQs.
          */
-        for_each_irq_desc(irq, desc)
+        for_each_irq_desc(irq, desc) {
+                if (!desc)
+                        continue;
+
                 register_irq_proc(irq, desc);
+        }
 }
 
diff --git a/kernel/irq/spurious.c b/kernel/irq/spurious.c
index dd364c11e56e..3738107531fd 100644
--- a/kernel/irq/spurious.c
+++ b/kernel/irq/spurious.c
@@ -91,6 +91,9 @@ static int misrouted_irq(int irq)
         int i, ok = 0;
 
         for_each_irq_desc(i, desc) {
+                if (!desc)
+                        continue;
+
                 if (!i)
                          continue;
 
@@ -112,6 +115,8 @@ static void poll_spurious_irqs(unsigned long dummy)
         for_each_irq_desc(i, desc) {
                 unsigned int status;
 
+                if (!desc)
+                        continue;
                 if (!i)
                          continue;