Avoid needlessly costly migrations. CONFIG_SCHED_CPU_AFFINITY

Given a choice between several available CPUs (unlinked) on which
to schedule a task, let the scheduler select the CPU closest to
where that task was previously scheduled.  Hopefully, this will
reduce cache migration penalties.

TODO: If a lower-priority task must be preempted and there are several
scheduled tasks with the same low priority, then preempt the closest.

1 files changed, 49 insertions, 0 deletions

diff --git a/litmus/affinity.c b/litmus/affinity.c
new file mode 100644
index 000000000000..9d5405cf05fd
--- /dev/null
+++ b/litmus/affinity.c
@@ -0,0 +1,49 @@
+#include <linux/cpu.h>
+
+#include <litmus/affinity.h>
+
+struct neighborhood neigh_info[NR_CPUS];
+
+/* called by _init_litmus() */
+void init_topology(void)
+{
+        int cpu;
+        int i;
+        int chk;
+        int depth = num_cache_leaves;
+
+        if(depth > MAX_CACHE_DEPTH) /* L4 and greater?? */
+                depth = MAX_CACHE_DEPTH;
+
+        for_each_online_cpu(cpu)
+        {
+                for(i = 0; i < (int)depth; ++i)
+                {
+                        long unsigned int firstbits;
+
+                        chk = get_shared_cpu_map((struct cpumask *)&neigh_info[cpu].neighbors[i], cpu, i);
+                        if(chk) /* failed */
+                        {
+                                neigh_info[cpu].size[i] = 0;
+                        }
+                        else
+                        {
+                                /* size = num bits in mask */
+                                neigh_info[cpu].size[i] = cpumask_weight((struct cpumask *)&neigh_info[cpu].neighbors[i]);
+                        }
+                        firstbits = *neigh_info[cpu].neighbors[i]->bits;
+                        printk("CPU %d has %d neighbors at level %d. (mask = %lx)\n",
+                                                        cpu, neigh_info[cpu].size[i], i, firstbits);
+                }
+
+                /* set data for non-existent levels */
+                for(; i < MAX_CACHE_DEPTH; ++i)
+                {
+                        neigh_info[cpu].size[i] = 0;
+
+                        printk("CPU %d has %d neighbors at level %d. (mask = %lx)\n",
+                                                        cpu, neigh_info[cpu].size[i], i, 0lu);
+                }
+        }
+}
+