kernel/irq/affinity.c

   1
   2 #include <linux/interrupt.h>
   3 #include <linux/kernel.h>
   4 #include <linux/slab.h>
   5 #include <linux/cpu.h>
   6
   7 static int get_first_sibling(unsigned int cpu)
   8 {
   9         unsigned int ret;
  10
  11         ret = cpumask_first(topology_sibling_cpumask(cpu));
  12         if (ret < nr_cpu_ids)
  13                 return ret;
  14         return cpu;
  15 }
  16
  17 /*
  18  * Take a map of online CPUs and the number of available interrupt vectors
  19  * and generate an output cpumask suitable for spreading MSI/MSI-X vectors
  20  * so that they are distributed as good as possible around the CPUs.  If
  21  * more vectors than CPUs are available we'll map one to each CPU,
  22  * otherwise we map one to the first sibling of each socket.
  23  *
  24  * If there are more vectors than CPUs we will still only have one bit
  25  * set per CPU, but interrupt code will keep on assigning the vectors from
  26  * the start of the bitmap until we run out of vectors.
  27  */
  28 struct cpumask *irq_create_affinity_mask(unsigned int *nr_vecs)
  29 {
  30         struct cpumask *affinity_mask;
  31         unsigned int max_vecs = *nr_vecs;
  32
  33         if (max_vecs == 1)
  34                 return NULL;
  35
  36         affinity_mask = kzalloc(cpumask_size(), GFP_KERNEL);
  37         if (!affinity_mask) {
  38                 *nr_vecs = 1;
  39                 return NULL;
  40         }
  41
  42         if (max_vecs >= num_online_cpus()) {
  43                 cpumask_copy(affinity_mask, cpu_online_mask);
  44                 *nr_vecs = num_online_cpus();
  45         } else {
  46                 unsigned int vecs = 0, cpu;
  47
  48                 for_each_online_cpu(cpu) {
  49                         if (cpu == get_first_sibling(cpu)) {
  50                                 cpumask_set_cpu(cpu, affinity_mask);
  51                                 vecs++;
  52                         }
  53
  54                         if (--max_vecs == 0)
  55                                 break;
  56                 }
  57                 *nr_vecs = vecs;
  58         }
  59
  60         return affinity_mask;
  61 }