[RFC] PCI_IRQ_AFFINITY limits MSI-X allocation on 384 CPU / 1000+ NVMe system

[santhosh kumar]

Observed:
- Linux 6.13
- 384 CPUs
- 1000+ NVMe devices


With PCI_IRQ_AFFINITY:
- some NVMe devices fail to obtain dedicated MSI-X vectors


Without PCI_IRQ_AFFINITY:
- all NVMe devices obtain 2 MSI-X vectors

Investigation suggests an interaction between:
- group_cpus_evenly()
- irq_create_affinity_masks()
- x86 vector allocation



Looking for feedback on whether affinity-constrained vector allocation
could explain this behavior.