[PATCH] genirq: Add default affinity mask command line option

[Thomas Gleixner]

From: Thomas Gleixner <t...@linutronix.de>
Date: Fri May 25 16:59:47 2012 +0200
Subject: genirq: Add default affinity mask command line option

If we isolate CPUs, then we don't want random device interrupts on them. Even
w/o the user space irq balancer enabled we can end up with irqs on non boot
cpus and chasing newly requested interrupts is a tedious task.

Allow to restrict the default irq affinity mask.

Signed-off-by: Thomas Gleixner <t...@linutronix.de>
---
 Documentation/kernel-parameters.txt |    9 +++++++++
 kernel/irq/irqdesc.c                |   21 +++++++++++++++++++--
 2 files changed, 28 insertions(+), 2 deletions(-)

--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1682,6 +1682,15 @@ bytes respectively. Such letter suffixes
        ip=             [IP_PNP]
                        See Documentation/filesystems/nfs/nfsroot.txt.
 
+       irqaffinity=    [SMP] Set the default irq affinity mask
+                       Format:
+                       <cpu number>,...,<cpu number>
+                       or
+                       <cpu number>-<cpu number>
+                       (must be a positive range in ascending order)
+                       or a mixture
+                       <cpu number>,...,<cpu number>-<cpu number>
+
        irqfixup        [HW]
                        When an interrupt is not handled search all handlers
                        for it. Intended to get systems with badly broken
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -24,10 +24,27 @@
 static struct lock_class_key irq_desc_lock_class;
 
 #if defined(CONFIG_SMP)
+static int __init irq_affinity_setup(char *str)
+{
+       zalloc_cpumask_var(&irq_default_affinity, GFP_NOWAIT);
+       cpulist_parse(str, irq_default_affinity);
+       /*
+        * Set at least the boot cpu. We don't want to end up with
+        * bugreports caused by random comandline masks
+        */
+       cpumask_set_cpu(smp_processor_id(), irq_default_affinity);
+       return 1;
+}
+__setup("irqaffinity=", irq_affinity_setup);
+
 static void __init init_irq_default_affinity(void)
 {
-       alloc_cpumask_var(&irq_default_affinity, GFP_NOWAIT);
-       cpumask_setall(irq_default_affinity);
+#ifdef CONFIG_CPUMASK_OFFSTACK
+       if (!irq_default_affinity)
+               zalloc_cpumask_var(&irq_default_affinity, GFP_NOWAIT);
+#endif
+       if (cpumask_empty(irq_default_affinity))
+               cpumask_setall(irq_default_affinity);
 }
 #else
 static void __init init_irq_default_affinity(void)