Messages in this thread Patch in this message | | | Subject | Re: [PATCH] cpu-topology: warn if NUMA configurations conflicts with lower layer | From | Valentin Schneider <> | Date | Sat, 11 Jan 2020 20:56:28 +0000 |
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On 09/01/2020 12:58, Zengtao (B) wrote: >> IIUC, the problem is that virt can set up a broken topology in some >> cases where MPIDR doesn't line up correctly with the defined NUMA >> nodes. >> >> We could argue that it is a qemu/virt problem, but it would be nice if >> we could at least detect it. The proposed patch isn't really the right >> solution as it warns on some valid topologies as Sudeep already pointed >> out. >> >> It sounds more like we need a mask subset check in the sched_domain >> building code, if there isn't already one? > > Currently no, it's a bit complex to do the check in the sched_domain building code, > I need to take a think of that. > Suggestion welcomed. >
Doing a search on the sched_domain spans themselves should look something like the completely untested:
---8<--- diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 6ec1e595b1d4..96128d12ec23 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -1879,6 +1879,43 @@ static struct sched_domain *build_sched_domain(struct sched_domain_topology_leve return sd; } +/* Ensure topology masks are sane; non-NUMA spans shouldn't overlap */ +static int validate_topology_spans(const struct cpumask *cpu_map) +{ + struct sched_domain_topology_level *tl; + int i, j; + + for_each_sd_topology(tl) { + /* NUMA levels are allowed to overlap */ + if (tl->flags & SDTL_OVERLAP) + break; + + /* + * Non-NUMA levels cannot partially overlap - they must be + * either equal or wholly disjoint. Otherwise we can end up + * breaking the sched_group lists - i.e. a later get_group() + * pass breaks the linking done for an earlier span. + */ + for_each_cpu(i, cpu_map) { + for_each_cpu(j, cpu_map) { + if (i == j) + continue; + /* + * We should 'and' all those masks with 'cpu_map' + * to exactly match the topology we're about to + * build, but that can only remove CPUs, which + * only lessens our ability to detect overlaps + */ + if (!cpumask_equal(tl->mask(i), tl->mask(j)) && + cpumask_intersects(tl->mask(i), tl->mask(j))) + return -1; + } + } + } + + return 0; +} + /* * Find the sched_domain_topology_level where all CPU capacities are visible * for all CPUs. @@ -1953,7 +1990,8 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att struct sched_domain_topology_level *tl_asym; bool has_asym = false; - if (WARN_ON(cpumask_empty(cpu_map))) + if (WARN_ON(cpumask_empty(cpu_map)) || + WARN_ON(validate_topology_spans(cpu_map))) goto error; alloc_state = __visit_domain_allocation_hell(&d, cpu_map); --->8--- Alternatively the assertion on the sched_group linking I suggested earlier in the thread should suffice, since this should trigger whenever we have overlapping non-NUMA sched domains.
Since you have a setup where you can reproduce the issue, could please give either (ideally both!) a try? Thanks.
> Thanks > Zengtao > >> >> Morten
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