59 lines
2.7 KiB
Plaintext
59 lines
2.7 KiB
Plaintext
PCI EXPANDER BRIDGE (PXB)
|
|
=========================
|
|
|
|
Description
|
|
===========
|
|
PXB is a "light-weight" host bridge in the same PCI domain
|
|
as the main host bridge whose purpose is to enable
|
|
the main host bridge to support multiple PCI root buses.
|
|
It is implemented only for i440fx and can be placed only
|
|
on bus 0 (pci.0).
|
|
|
|
As opposed to PCI-2-PCI bridge's secondary bus, PXB's bus
|
|
is a primary bus and can be associated with a NUMA node
|
|
(different from the main host bridge) allowing the guest OS
|
|
to recognize the proximity of a pass-through device to
|
|
other resources as RAM and CPUs.
|
|
|
|
Usage
|
|
=====
|
|
A detailed command line would be:
|
|
|
|
[qemu-bin + storage options]
|
|
-m 2G
|
|
-object memory-backend-ram,size=1024M,policy=bind,host-nodes=0,id=ram-node0 -numa node,nodeid=0,cpus=0,memdev=ram-node0
|
|
-object memory-backend-ram,size=1024M,policy=bind,host-nodes=1,id=ram-node1 -numa node,nodeid=1,cpus=1,memdev=ram-node1
|
|
-device pxb,id=bridge1,bus=pci.0,numa_node=1,bus_nr=4 -netdev user,id=nd -device e1000,bus=bridge1,addr=0x4,netdev=nd
|
|
-device pxb,id=bridge2,bus=pci.0,numa_node=0,bus_nr=8 -device e1000,bus=bridge2,addr=0x3
|
|
-device pxb,id=bridge3,bus=pci.0,bus_nr=40 -drive if=none,id=drive0,file=[img] -device virtio-blk-pci,drive=drive0,scsi=off,bus=bridge3,addr=1
|
|
|
|
Here you have:
|
|
- 2 NUMA nodes for the guest, 0 and 1. (both mapped to the same NUMA node in host, but you can and should put it in different host NUMA nodes)
|
|
- a pxb host bridge attached to NUMA 1 with an e1000 behind it
|
|
- a pxb host bridge attached to NUMA 0 with an e1000 behind it
|
|
- a pxb host bridge not attached to any NUMA with a hard drive behind it.
|
|
|
|
Limitations
|
|
===========
|
|
Please observe that we specified the bus "pci.0" for the second and third pxb.
|
|
This is because when no bus is given, another pxb can be selected by QEMU as default bus,
|
|
however, PXBs can be placed only under the root bus.
|
|
|
|
Implementation
|
|
==============
|
|
The PXB is composed by:
|
|
- HostBridge (TYPE_PXB_HOST)
|
|
The host bridge allows to register and query the PXB's PCI root bus in QEMU.
|
|
- PXBDev(TYPE_PXB_DEVICE)
|
|
It is a regular PCI Device that resides on the piix host-bridge bus and its bus uses the same PCI domain.
|
|
However, the bus behind is exposed through ACPI as a primary PCI bus and starts a new PCI hierarchy.
|
|
The interrupts from devices behind the PXB are routed through this device the same as if it were a
|
|
PCI-2-PCI bridge. The _PRT follows the i440fx model.
|
|
- PCIBridgeDev(TYPE_PCI_BRIDGE_DEV)
|
|
Created automatically as part of init sequence.
|
|
When adding a device to PXB it is attached to the bridge for two reasons:
|
|
- Using the bridge will enable hotplug support
|
|
- All the devices behind the bridge will use bridge's IO/MEM windows compacting
|
|
the PCI address space.
|
|
|