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Message-ID: <175162039637.406.8610358723761872462.tip-bot2@tip-bot2>
Date: Fri, 04 Jul 2025 09:13:16 -0000
From: "tip-bot2 for K Prateek Nayak" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Leon Romanovsky <leon@...nel.org>,
Valentin Schneider <vschneid@...hat.com>,
K Prateek Nayak <kprateek.nayak@....com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Steve Wahl <steve.wahl@....com>, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: sched/urgent] sched/fair: Use sched_domain_span() for
topology_span_sane()
The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: 02bb4259ca525efa39a2531cb630329fb87fc968
Gitweb: https://git.kernel.org/tip/02bb4259ca525efa39a2531cb630329fb87fc968
Author: K Prateek Nayak <kprateek.nayak@....com>
AuthorDate: Mon, 30 Jun 2025 06:10:59
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 04 Jul 2025 10:35:56 +02:00
sched/fair: Use sched_domain_span() for topology_span_sane()
Leon noted a topology_span_sane() warning in their guest deployment
starting from v6.16-rc1 [1]. Debug that followed pointed to the
tl->mask() for the NODE domain being incorrectly resolved to that of the
highest NUMA domain.
tl->mask() for NODE is set to the sd_numa_mask() which depends on the
global "sched_domains_curr_level" hack. "sched_domains_curr_level" is
set to the "tl->numa_level" during tl traversal in build_sched_domains()
calling sd_init() but was not reset before topology_span_sane().
Since "tl->numa_level" still reflected the old value from
build_sched_domains(), topology_span_sane() for the NODE domain trips
when the span of the last NUMA domain overlaps.
Instead of replicating the "sched_domains_curr_level" hack, Valentin
suggested using the spans from the sched_domain objects constructed
during build_sched_domains() which can also catch overlaps when the
domain spans are fixed up by build_sched_domain().
The original warning was reproducble on the follwoing NUMA topology
reported by Leon:
$ sudo numactl -H
available: 5 nodes (0-4)
node 0 cpus: 0 1
node 0 size: 2927 MB
node 0 free: 1603 MB
node 1 cpus: 2 3
node 1 size: 3023 MB
node 1 free: 3008 MB
node 2 cpus: 4 5
node 2 size: 3023 MB
node 2 free: 3007 MB
node 3 cpus: 6 7
node 3 size: 3023 MB
node 3 free: 3002 MB
node 4 cpus: 8 9
node 4 size: 3022 MB
node 4 free: 2718 MB
node distances:
node 0 1 2 3 4
0: 10 39 38 37 36
1: 39 10 38 37 36
2: 38 38 10 37 36
3: 37 37 37 10 36
4: 36 36 36 36 10
The above topology can be mimicked using the following QEMU cmd that was
used to reproduce the warning and test the fix:
sudo qemu-system-x86_64 -enable-kvm -cpu host \
-m 20G -smp cpus=10,sockets=10 -machine q35 \
-object memory-backend-ram,size=4G,id=m0 \
-object memory-backend-ram,size=4G,id=m1 \
-object memory-backend-ram,size=4G,id=m2 \
-object memory-backend-ram,size=4G,id=m3 \
-object memory-backend-ram,size=4G,id=m4 \
-numa node,cpus=0-1,memdev=m0,nodeid=0 \
-numa node,cpus=2-3,memdev=m1,nodeid=1 \
-numa node,cpus=4-5,memdev=m2,nodeid=2 \
-numa node,cpus=6-7,memdev=m3,nodeid=3 \
-numa node,cpus=8-9,memdev=m4,nodeid=4 \
-numa dist,src=0,dst=1,val=39 \
-numa dist,src=0,dst=2,val=38 \
-numa dist,src=0,dst=3,val=37 \
-numa dist,src=0,dst=4,val=36 \
-numa dist,src=1,dst=0,val=39 \
-numa dist,src=1,dst=2,val=38 \
-numa dist,src=1,dst=3,val=37 \
-numa dist,src=1,dst=4,val=36 \
-numa dist,src=2,dst=0,val=38 \
-numa dist,src=2,dst=1,val=38 \
-numa dist,src=2,dst=3,val=37 \
-numa dist,src=2,dst=4,val=36 \
-numa dist,src=3,dst=0,val=37 \
-numa dist,src=3,dst=1,val=37 \
-numa dist,src=3,dst=2,val=37 \
-numa dist,src=3,dst=4,val=36 \
-numa dist,src=4,dst=0,val=36 \
-numa dist,src=4,dst=1,val=36 \
-numa dist,src=4,dst=2,val=36 \
-numa dist,src=4,dst=3,val=36 \
...
Closes: https://lore.kernel.org/lkml/20250610110701.GA256154@unreal/ [1]
Fixes: ccf74128d66c ("sched/topology: Assert non-NUMA topology masks don't (partially) overlap") # ce29a7da84cd, f55dac1dafb3
Reported-by: Leon Romanovsky <leon@...nel.org>
Suggested-by: Valentin Schneider <vschneid@...hat.com>
Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Steve Wahl <steve.wahl@....com>
Reviewed-by: Valentin Schneider <vschneid@...hat.com>
Tested-by: Valentin Schneider <vschneid@...hat.com>
Link: https://lore.kernel.org/r/20250630061059.1547-1-kprateek.nayak@amd.com
---
kernel/sched/topology.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index b958fe4..0e46068 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -2403,6 +2403,7 @@ static bool topology_span_sane(const struct cpumask *cpu_map)
id_seen = sched_domains_tmpmask2;
for_each_sd_topology(tl) {
+ struct sd_data *sdd = &tl->data;
/* NUMA levels are allowed to overlap */
if (tl->flags & SDTL_OVERLAP)
@@ -2418,22 +2419,24 @@ static bool topology_span_sane(const struct cpumask *cpu_map)
* breaks the linking done for an earlier span.
*/
for_each_cpu(cpu, cpu_map) {
- const struct cpumask *tl_cpu_mask = tl->mask(cpu);
+ struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu);
+ struct cpumask *sd_span = sched_domain_span(sd);
int id;
/* lowest bit set in this mask is used as a unique id */
- id = cpumask_first(tl_cpu_mask);
+ id = cpumask_first(sd_span);
if (cpumask_test_cpu(id, id_seen)) {
- /* First CPU has already been seen, ensure identical spans */
- if (!cpumask_equal(tl->mask(id), tl_cpu_mask))
+ /* First CPU has already been seen, ensure identical sd spans */
+ sd = *per_cpu_ptr(sdd->sd, id);
+ if (!cpumask_equal(sched_domain_span(sd), sd_span))
return false;
} else {
/* First CPU hasn't been seen before, ensure it's a completely new span */
- if (cpumask_intersects(tl_cpu_mask, covered))
+ if (cpumask_intersects(sd_span, covered))
return false;
- cpumask_or(covered, covered, tl_cpu_mask);
+ cpumask_or(covered, covered, sd_span);
cpumask_set_cpu(id, id_seen);
}
}
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