Force virtiofs devices to a single virtio queue (vcpus=1)#40758
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asherkariv wants to merge 1 commit into
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Force virtiofs devices to a single virtio queue (vcpus=1)#40758asherkariv wants to merge 1 commit into
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Pull request overview
This PR passes the WSL VM’s vCPU count to wsldevicehost.dll by appending a vcpus=<count> token (semicolon-delimited) to the virtiofs mount/device options string, reusing the existing device-options pathway (already used for swiotlb).
Changes:
wsl: Appendvcpus={ProcessorCount}to the effective virtiofs mount options inWslCoreVm::AddVirtioFsSharewhenProcessorCount != 0.wslc: Cache avcpus={CpuCount}token inHcsVirtualMachineand append it to the virtiofs device options inAddShare.- Introduce a new
m_vcpusOptionmember to carry the token through the wslc path similarly tom_swiotlbOption.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| src/windows/service/exe/WslCoreVm.cpp | Appends vcpus=<count> to virtiofs mount options in the core WSL VM virtiofs share path. |
| src/windows/service/exe/HcsVirtualMachine.h | Adds m_vcpusOption member to store the vCPU-count token for wsldevicehost. |
| src/windows/service/exe/HcsVirtualMachine.cpp | Initializes and appends the cached vcpus=<count> token when creating virtiofs shares. |
benhillis
reviewed
Jun 9, 2026
benhillis
reviewed
Jun 9, 2026
Add a vcpus=1 token to the virtiofs device-options string so each device
exposes a single virtio queue. This bounds the number of concurrent
guest-memory apertures the device can request, avoiding the host VID's
512-aperture quota that wsldevicehost otherwise livelocks against when
servicing many parallel requests.
- Define a shared c_vcpusOption ("vcpus=1") constant in
GuestDeviceManager.h, with a TODO to revisit once the devicehost
supports multiple shares per device.
- HcsVirtualMachine::AddShare and WslCoreVm::AddVirtioFsShare append the
swiotlb and vcpus tokens via a small appendOption lambda, covering the
fixed-drive, dynamic-add, and remount paths. Both tokens are constant
for the VM's lifetime, so duplicates collapse to a single VirtioFsShare
map entry.
- Bump Microsoft.WSL.DeviceHost to 1.2.32-0.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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| // Append swiotlb and vcpus here to cover the fixed-drive, dynamic add, and remount paths. | ||
| // Safe to duplicate: both tokens are constant per VM, and VirtioFsShare collapses repeats into one map entry. | ||
| std::wstring effectiveOptions(Options); | ||
| if (!m_swiotlbOption.empty()) | ||
| { | ||
| auto appendOption = [&effectiveOptions](const std::wstring& option) { | ||
| if (option.empty()) |
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Summary of the Pull Request
Force each virtiofs device to a single virtio queue by adding a
vcpus=1token to the virtiofs device-options string. This bounds the number of concurrent guest-memory apertures a device can request, avoiding the host VID's 512-aperture quota thatwsldevicehostotherwise livelocks against when servicing many parallel requests.The token reuses the existing device-options channel already used to pass the
swiotlbinformation, so no new IPC path or message format is introduced.Detailed Description of the Pull Request / Additional comments
c_vcpusOption("vcpus=1") constant inGuestDeviceManager.h, with a TODO to revisit once the devicehost supports multiple shares per device.HcsVirtualMachine::AddShare(wslc) andWslCoreVm::AddVirtioFsShare(wsl) append theswiotlbandvcpustokens via a smallappendOptionlambda, covering the fixed-drive, dynamic-add, and remount paths.VirtioFsShareparses the options into a map.Microsoft.WSL.DeviceHostto1.2.32-0.PR Checklist
Validation Steps Performed
Manually validated that virtiofs
/mnt/cshares come up with thevcpus=1option across fixed-drive, dynamic-add, and remount paths, and thatwsldevicehostno longer exhausts the host VID aperture quota under parallel load.