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Enable automatic vNUMA for large WSL VMs - #41741
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Add the HCS NUMA topology object so HCS can derive a supported virtual topology for large processor counts instead of requiring WSL to clamp the VM to 256 processors. Co-authored-by: Copilot <[email protected]> Copilot-Session: ea0c67c5-0211-479b-a7b5-59aebb19b71c
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Copilot review overview
🟡 Changes recommended
The vNUMA setting must be gated to supported Windows builds to avoid VM creation regressions on older systems.
Review effort: Balanced
Findings: 2
Open (2)
What changed in this PR
Enables automatic HCS-derived vNUMA topology for large WSL and WSLC virtual machines.
Changes:
- Adds optional NUMA serialization to the local HCS schema.
- Enables automatic vNUMA for WSL and WSLC VMs.
- Adds serialization and large-host processor-count coverage.
| File | Description |
|---|---|
src/windows/common/hcs_schema.h |
Adds optional NUMA topology serialization. |
src/windows/service/exe/WslCoreVm.cpp |
Enables automatic vNUMA for WSL VMs. |
src/windows/service/exe/HcsVirtualMachine.cpp |
Enables automatic vNUMA for WSLC VMs. |
test/windows/HcsSchemaUnitTests.cpp |
Tests empty NUMA object serialization. |
test/windows/UnitTests.cpp |
Tests processor counts above 256. |
test/windows/CMakeLists.txt |
Registers the new schema test source. |
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Preserve the existing single-node HCS configuration on older Windows builds where vNUMA topology creation is unsupported. Co-authored-by: Copilot <[email protected]> Copilot-Session: ea0c67c5-0211-479b-a7b5-59aebb19b71c
Co-authored-by: Copilot <[email protected]> Copilot-Session: ea0c67c5-0211-479b-a7b5-59aebb19b71c
1 of 2 tasks
Ben Hillis (benhillis)
marked this pull request as ready for review
October 1, 2026 00:02
Ben Hillis (benhillis)
enabled auto-merge (squash)
October 2, 2026 00:49
Blue (OneBlue)
approved these changes
Oct 2, 2026
| OMIT_IF_EMPTY(j, processor, EnablePerfmonLbr) | ||
| } | ||
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| struct Numa |
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nit: We can reuse EmptyObject for this
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Summary
Enable automatic virtual NUMA topology generation for WSL virtual machines on Windows build 26100 and newer.
WSL previously omitted
ComputeTopology.Numafrom its HCS configuration. HCS therefore treated the VM as a single virtual NUMA node/socket, which fails when the requested processor count exceeds the supported per-socket topology. Emitting an emptyNumaobject asks HCS to derive the virtual topology from the requested resources and physical host topology.This change:
Validation
wslteststarget successfully.Numatopology, and HCS rejected the single-node configuration withMaxVpCountPerSocketLimit: 256andmaxVpCountPerSocket: 384.Fixes #41731