linux.conf.au, January 2003
      PROGRAMMING: kernel/softirq.c

 	/*
 	   - No shared variables, all the data are CPU local.
 	   - If a softirq needs serialization, let it serialize itself
 	     by its own spinlocks.
 	   - Even if softirq is serialized, only local cpu is marked for
 	     execution. Hence, we get something sort of weak cpu binding.
 	     Though it is still not clear, will it result in better locality
 	     or will not.
 	
 	   Examples:
 	   - NET RX softirq. It is multithreaded and does not require
 	     any global serialization.
 	   - NET TX softirq. It kicks software netdevice queues, hence
 	     it is logically serialized per device, but this serialization
 	     is invisible to common code.
 	   - Tasklets: serialized wrt itself.
 	   - Bottom halves: globally serialized, grr...
 	 */
 	
 	irq_cpustat_t irq_stat[NR_CPUS];
 	
 	static struct softirq_action softirq_vec[32] __cacheline_aligned_in_smp;