From: Rik van Riel <[email protected]> On systems with complex NUMA topologies, the node scoring is adjusted to allow workloads to converge on nodes that are near each other.
The way a task group's preferred nid is determined needs to be adjusted, in order for the preferred_nid to be consistent with group_weight scoring. This ensures that we actually try to converge workloads on adjacent nodes. Signed-off-by: Rik van Riel <[email protected]> Tested-by: Chegu Vinod <[email protected]> --- kernel/sched/fair.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 87 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 6df460f..b973d77 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1648,6 +1648,92 @@ static u64 numa_get_avg_runtime(struct task_struct *p, u64 *period) return delta; } +/* + * Determine the preferred nid for a task in a numa_group. This needs to + * be done in a way that produces consistent results with group_weight, + * otherwise workloads might not converge. + */ +static int preferred_group_nid(struct task_struct *p, int nid) +{ + nodemask_t nodes; + int dist; + + /* Direct connections between all NUMA nodes. */ + if (sched_numa_topology_type == NUMA_DIRECT) + return nid; + + /* + * On a system with glueless mesh NUMA topology, group_weight + * scores nodes according to the number of NUMA hinting faults on + * both the node itself, and on nearby nodes. + */ + if (sched_numa_topology_type == NUMA_GLUELESS_MESH) { + unsigned long score, max_score = 0; + int node, max_node = nid; + + dist = sched_max_numa_distance; + + for_each_online_node(node) { + score = group_weight(p, node, dist); + if (score > max_score) { + max_score = score; + max_node = node; + } + } + return max_node; + } + + /* + * Finding the preferred nid in a system with NUMA backplane + * interconnect topology is more involved. The goal is to locate + * tasks from numa_groups near each other in the system, and + * untangle workloads from different sides of the system. This requires + * searching down the hierarchy of node groups, recursively searching + * inside the highest scoring group of nodes. The nodemask tricks + * keep the complexity of the search down. + */ + nodes = node_online_map; + for (dist = sched_max_numa_distance; dist > LOCAL_DISTANCE; dist--) { + unsigned long max_faults = 0; + nodemask_t max_group; + int a, b; + + /* Are there nodes at this distance from each other? */ + if (!find_numa_distance(dist)) + continue; + + for_each_node_mask(a, nodes) { + unsigned long faults = 0; + nodemask_t this_group; + nodes_clear(this_group); + + /* Sum group's NUMA faults; includes a==b case. */ + for_each_node_mask(b, nodes) { + if (node_distance(a, b) < dist) { + faults += group_faults(p, b); + node_set(b, this_group); + node_clear(b, nodes); + } + } + + /* Remember the top group. */ + if (faults > max_faults) { + max_faults = faults; + max_group = this_group; + /* + * subtle: at the smallest distance there is + * just one node left in each "group", the + * winner is the preferred nid. + */ + nid = a; + } + } + /* Next round, evaluate the nodes within max_group. */ + nodes = max_group; + } + return nid; +} + static void task_numa_placement(struct task_struct *p) { int seq, nid, max_nid = -1, max_group_nid = -1; @@ -1730,7 +1816,7 @@ static void task_numa_placement(struct task_struct *p) if (p->numa_group) { update_numa_active_node_mask(p->numa_group); spin_unlock_irq(group_lock); - max_nid = max_group_nid; + max_nid = preferred_group_nid(p, max_group_nid); } if (max_faults) { -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
