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>

1 files changed, 8 insertions, 4 deletions

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());