Signed-off-by: Marcel Apfelbaum marcel@redhat.com --- docs/pci_expander_bridge.txt | 52 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 52 insertions(+) create mode 100644 docs/pci_expander_bridge.txt
diff --git a/docs/pci_expander_bridge.txt b/docs/pci_expander_bridge.txt new file mode 100644 index 0000000..58bf7a8 --- /dev/null +++ b/docs/pci_expander_bridge.txt @@ -0,0 +1,52 @@ +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. + +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] +-bios [seabios-dir]/out/bios.bin -L [seabios-dir]/out/ +-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=interleave,host-nodes=0,id=ram-node1 -numa node,nodeid=1,cpus=1,memdev=ram-node1 +-device pxb-device,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-device,id=bridge2,bus=pci.0,numa_node=0,bus_nr=8 -device e1000,bus=bridge2,addr=0x3 +-device pxb-device,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. + +Implementation +============== +The PXB is composed by: +- HostBridge (TYPE_PXB_HOST) + The host bridge allows to register and query the PXB's rPCI 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. +