* Mel Gorman <mgor...@techsingularity.net> [2018-09-07 11:11:38]: > task_numa_migrate is responsible for finding a core on a preferred NUMA > node for a task. As part of this, task_numa_find_cpu iterates through > the CPUs of a node and evaulates CPUs, both idle and with running tasks, > as placement candidates. Generally though, any idle CPU is equivalent in > terms of improving imbalances and a search after finding one is pointless. > This patch stops examining CPUs on a node if an idle CPU is considered > suitable. >
However there can be a thread on the destination node that might benefit from swapping with the current thread. Don't we loose that opportunity to swap if skip checking for other threads? To articulate. Thread A currently running on node 0 wants to move to node 1. Thread B currently running on node 1 is better of if it ran on node 0. Thread A seems idle cpu before seeing Thread B; skips and looses an opportunity to swap. Eventually thread B will get an opportunity to move to node 0, when thread B calls task_numa_placement but we are probably stopping it from achieving earlier. -- Thanks and Regards Srikar Dronamraju
