Regression in IXGBE(4) on 12.0-RELEASE?

[Greg Rivers]

These Intel NICs have been performing very well for me:

ix0 at pci0:7:0:0:	class=0x020000 card=0x17d3103c chip=0x10fb8086 rev=0x01 hdr=0x00
    vendor     = 'Intel Corporation'
    device     = '82599ES 10-Gigabit SFI/SFP+ Network Connection'
    class      = network
    subclass   = ethernet

On 11.2-RELEASE, the cards probe like this:

ix0: <Intel(R) PRO/10GbE PCI-Express Network Driver, Version - 3.2.12-k> port 0x7000-0x701f mem 0xf7f00000-0xf7ffffff,0xf7ef0000-0xf7ef3fff irq 28 at device 0.0 numa-domain 0 on pci1
ix0: Using MSI-X interrupts with 9 vectors
ix0: Ethernet address: 8c:dc:d4:af:8a:e0
ix0: PCI Express Bus: Speed 5.0GT/s Width x8
ix0: netmap queues/slots: TX 8/2048, RX 8/2048

As expected, all 8 queues are enabled on the NIC, with 8 corresponding interrupt threads pinned to 8 different CPUs

But on 12.0-RELEASE, the cards probe like this:

ix0: <Intel(R) PRO/10GbE PCI-Express Network Driver> port 0x4020-0x403f mem 0xe2900000-0xe29fffff,0xe2a04000-0xe2a07fff at device 0.0 numa-domain 0 on pci4
ix0: using 2048 tx descriptors and 2048 rx descriptors
ix0: msix_init qsets capped at 16
ix0: Unable to map MSIX table 
ix0: Using an MSI interrupt
ix0: allocated for 1 queues
ix0: allocated for 1 rx queues
ix0: Ethernet address: 48:df:37:62:be:38
ix0: PCI Express Bus: Speed 5.0GT/s Width x8
ix0: netmap queues/slots: TX 1/2048, RX 1/2048
ix0: link state changed to UP

MSI-X is disabled, and only one queue is enabled. I'm sure this is going to perform poorly under high network loads. Does anyone know why this is?

-- 
Greg Rivers