sched/numa: Ensure task_numa_migrate() checks the preferred node
The first thing task_numa_migrate() does is check to see if there is CPU capacity available on the preferred node, in order to move the task there. However, if the preferred node is all busy, we would skip considering that node for tasks swaps in the subsequent loop. This prevents NUMA convergence of tasks on busy systems. However, swapping locations with a task on our preferred nid, when the preferred nid is busy, is perfectly fine. The fix is to also look for a CPU on our preferred nid when it is totally busy. This changes "perf bench numa mem -p 4 -t 20 -m -0 -P 1000" from not converging in 15 minutes on my 4 node system, to converging in 10-20 seconds. Signed-off-by: Rik van Riel <riel@redhat.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: mgorman@suse.de Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/20140604160942.6969b101@cuia.bos.redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -1302,9 +1302,8 @@ static int task_numa_migrate(struct task_struct *p)
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groupimp = group_weight(p, env.dst_nid) - groupweight;
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groupimp = group_weight(p, env.dst_nid) - groupweight;
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update_numa_stats(&env.dst_stats, env.dst_nid);
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update_numa_stats(&env.dst_stats, env.dst_nid);
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/* If the preferred nid has free capacity, try to use it. */
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/* Try to find a spot on the preferred nid. */
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if (env.dst_stats.has_free_capacity)
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task_numa_find_cpu(&env, taskimp, groupimp);
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task_numa_find_cpu(&env, taskimp, groupimp);
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/* No space available on the preferred nid. Look elsewhere. */
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/* No space available on the preferred nid. Look elsewhere. */
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if (env.best_cpu == -1) {
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if (env.best_cpu == -1) {
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