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Date: Mon, 09 Aug 2021 13:52:38 +0100 From: Valentin Schneider <valentin.schneider@....com> To: Srikar Dronamraju <srikar@...ux.vnet.ibm.com> Cc: Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Michael Ellerman <mpe@...erman.id.au>, LKML <linux-kernel@...r.kernel.org>, Mel Gorman <mgorman@...hsingularity.net>, Rik van Riel <riel@...riel.com>, Thomas Gleixner <tglx@...utronix.de>, Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>, linuxppc-dev@...ts.ozlabs.org, Nathan Lynch <nathanl@...ux.ibm.com>, Gautham R Shenoy <ego@...ux.vnet.ibm.com>, Geetika Moolchandani <Geetika.Moolchandani1@....com>, Laurent Dufour <ldufour@...ux.ibm.com> Subject: Re: [PATCH v2 1/2] sched/topology: Skip updating masks for non-online nodes On 09/08/21 12:22, Srikar Dronamraju wrote: > * Valentin Schneider <valentin.schneider@....com> [2021-08-08 16:56:47]: >> Wait, doesn't the distance matrix (without any offline node) say >> >> distance(0, 3) == 40 >> >> ? We should have at the very least: >> >> node 0 1 2 3 >> 0: 10 20 ?? 40 >> 1: 20 20 ?? 40 >> 2: ?? ?? ?? ?? >> 3: 40 40 ?? 10 >> > > Before onlining node 3 and CPU 3 (node/CPU 0 and 1 are already online) > Note: Node 2-7 and CPU 2-7 are still offline. > > node 0 1 2 3 > 0: 10 20 40 10 > 1: 20 20 40 10 > 2: 40 40 10 10 > 3: 10 10 10 10 > > NODE->mask(0) == 0 > NODE->mask(1) == 1 > NODE->mask(2) == 0 > NODE->mask(3) == 0 > > Note: This is with updating Node 2's distance as 40 for figuring out > the number of numa levels. Since we have all possible distances, we > dont update Node 3 distance, so it will be as if its local to node 0. > > Now when Node 3 and CPU 3 are onlined > Note: Node 2, 3-7 and CPU 2, 3-7 are still offline. > > node 0 1 2 3 > 0: 10 20 40 40 > 1: 20 20 40 40 > 2: 40 40 10 40 > 3: 40 40 40 10 > > NODE->mask(0) == 0 > NODE->mask(1) == 1 > NODE->mask(2) == 0 > NODE->mask(3) == 0,3 > > CPU 0 continues to be part of Node->mask(3) because when we online and > we find the right distance, there is no API to reset the numa mask of > 3 to remove CPU 0 from the numa masks. > > If we had an API to clear/set sched_domains_numa_masks[node][] when > the node state changes, we could probably plug-in to clear/set the > node masks whenever node state changes. > Gotcha, this is now coming back to me... [...] >> Ok, so it looks like we really can't do without that part - even if we get >> "sensible" distance values for the online nodes, we can't divine values for >> the offline ones. >> > > Yes > Argh, while your approach does take care of the masks, it leaves sched_numa_topology_type unchanged. You *can* force an update of it, but yuck :( I got to the below... --- From: Srikar Dronamraju <srikar@...ux.vnet.ibm.com> Date: Thu, 1 Jul 2021 09:45:51 +0530 Subject: [PATCH 1/1] sched/topology: Skip updating masks for non-online nodes The scheduler currently expects NUMA node distances to be stable from init onwards, and as a consequence builds the related data structures once-and-for-all at init (see sched_init_numa()). Unfortunately, on some architectures node distance is unreliable for offline nodes and may very well change upon onlining. Skip over offline nodes during sched_init_numa(). Track nodes that have been onlined at least once, and trigger a build of a node's NUMA masks when it is first onlined post-init. Reported-by: Geetika Moolchandani <Geetika.Moolchandani1@....com> Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com> Signed-off-by: Valentin Schneider <valentin.schneider@....com> --- kernel/sched/topology.c | 65 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 65 insertions(+) diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index b77ad49dc14f..cba95793a9b7 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -1482,6 +1482,8 @@ int sched_max_numa_distance; static int *sched_domains_numa_distance; static struct cpumask ***sched_domains_numa_masks; int __read_mostly node_reclaim_distance = RECLAIM_DISTANCE; + +static unsigned long __read_mostly *sched_numa_onlined_nodes; #endif /* @@ -1833,6 +1835,16 @@ void sched_init_numa(void) sched_domains_numa_masks[i][j] = mask; for_each_node(k) { + /* + * Distance information can be unreliable for + * offline nodes, defer building the node + * masks to its bringup. + * This relies on all unique distance values + * still being visible at init time. + */ + if (!node_online(j)) + continue; + if (sched_debug() && (node_distance(j, k) != node_distance(k, j))) sched_numa_warn("Node-distance not symmetric"); @@ -1886,6 +1898,53 @@ void sched_init_numa(void) sched_max_numa_distance = sched_domains_numa_distance[nr_levels - 1]; init_numa_topology_type(); + + sched_numa_onlined_nodes = bitmap_alloc(nr_node_ids, GFP_KERNEL); + if (!sched_numa_onlined_nodes) + return; + + bitmap_zero(sched_numa_onlined_nodes, nr_node_ids); + for_each_online_node(i) + bitmap_set(sched_numa_onlined_nodes, i, 1); +} + +void __sched_domains_numa_masks_set(unsigned int node) +{ + int i, j; + + /* + * NUMA masks are not built for offline nodes in sched_init_numa(). + * Thus, when a CPU of a never-onlined-before node gets plugged in, + * adding that new CPU to the right NUMA masks is not sufficient: the + * masks of that CPU's node must also be updated. + */ + if (test_bit(node, sched_numa_onlined_nodes)) + return; + + bitmap_set(sched_numa_onlined_nodes, node, 1); + + for (i = 0; i < sched_domains_numa_levels; i++) { + for (j = 0; j < nr_node_ids; j++) { + if (!node_online(j) || node == j) + continue; + + if (node_distance(j, node) > sched_domains_numa_distance[i]) + continue; + + /* Add remote nodes in our masks */ + cpumask_or(sched_domains_numa_masks[i][node], + sched_domains_numa_masks[i][node], + sched_domains_numa_masks[0][j]); + } + } + + /* + * A new node has been brought up, potentially changing the topology + * classification. + * + * Note that this is racy vs any use of sched_numa_topology_type :/ + */ + init_numa_topology_type(); } void sched_domains_numa_masks_set(unsigned int cpu) @@ -1893,8 +1952,14 @@ void sched_domains_numa_masks_set(unsigned int cpu) int node = cpu_to_node(cpu); int i, j; + __sched_domains_numa_masks_set(node); + for (i = 0; i < sched_domains_numa_levels; i++) { for (j = 0; j < nr_node_ids; j++) { + if (!node_online(j)) + continue; + + /* Set ourselves in the remote node's masks */ if (node_distance(j, node) <= sched_domains_numa_distance[i]) cpumask_set_cpu(cpu, sched_domains_numa_masks[i][j]); } -- 2.25.1
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