irq: Better struct irqaction layout

We currently use kmalloc-96 slab for struct irqaction allocations on
64bit arches.

This is unfortunate because of possible false sharing and two cache
lines accesses.

Move 'name' and 'dir' fields at the end of the structure, and force a
suitable alignement.

Hot path fields now use one cache line on x86_64.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Reviewed-by: Andi Kleen <andi@firstfloor.org>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <1288865628.2659.69.camel@edumazet-laptop>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

include/linux/interrupt.h

@@ -114,15 +114,15 @@ typedef irqreturn_t (*irq_handler_t)(int, void *);
 struct irqaction {
 	irq_handler_t handler;
 	unsigned long flags;
-	const char *name;
 	void *dev_id;
 	struct irqaction *next;
 	int irq;
-	struct proc_dir_entry *dir;
 	irq_handler_t thread_fn;
 	struct task_struct *thread;
 	unsigned long thread_flags;
-};
+	const char *name;
+	struct proc_dir_entry *dir;
+} ____cacheline_internodealigned_in_smp;
 
 extern irqreturn_t no_action(int cpl, void *dev_id);