From: Long Li <[email protected]> Sent: Monday, March 16, 2026 2:08 PM > > When hv_pci_assign_numa_node() processes a device that does not have > HV_PCI_DEVICE_FLAG_NUMA_AFFINITY set or has an out-of-range > virtual_numa_node, the device NUMA node is left unset. On x86_64, > the uninitialized default happens to be 0, but on ARM64 it is > NUMA_NO_NODE (-1). > > Tests show that when no NUMA information is available from the Hyper-V > host, devices perform best when assigned to node 0. With NUMA_NO_NODE > the kernel may spread work across NUMA nodes, which degrades > performance on Hyper-V, particularly for high-throughput devices like > MANA. > > Always set the device NUMA node to 0 before the conditional NUMA > affinity check, so that devices get a performant default when the host > provides no NUMA information, and behavior is consistent on both > x86_64 and ARM64. > > Fixes: 999dd956d838 ("PCI: hv: Add support for protocol 1.3 and support > PCI_BUS_RELATIONS2") > Signed-off-by: Long Li <[email protected]>
Looks good. Reviewed-by: Michael Kelley <[email protected]> > --- > Changes in v2: > - Rewrite commit message to focus on performance as the primary > motivation: NUMA_NO_NODE causes the kernel to spread work across > NUMA nodes, degrading performance on Hyper-V > > drivers/pci/controller/pci-hyperv.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/drivers/pci/controller/pci-hyperv.c > b/drivers/pci/controller/pci-hyperv.c > index 2c7a406b4ba8..38a790f642a1 100644 > --- a/drivers/pci/controller/pci-hyperv.c > +++ b/drivers/pci/controller/pci-hyperv.c > @@ -2485,6 +2485,14 @@ static void hv_pci_assign_numa_node(struct > hv_pcibus_device *hbus) > if (!hv_dev) > continue; > > + /* > + * If the Hyper-V host doesn't provide a NUMA node for the > + * device, default to node 0. With NUMA_NO_NODE the kernel > + * may spread work across NUMA nodes, which degrades > + * performance on Hyper-V. > + */ > + set_dev_node(&dev->dev, 0); > + > if (hv_dev->desc.flags & HV_PCI_DEVICE_FLAG_NUMA_AFFINITY && > hv_dev->desc.virtual_numa_node < num_possible_nodes()) > /* > -- > 2.43.0 >
