On Tue, Mar 10, 2015 at 05:32:14PM +0200, Marcel Apfelbaum wrote: > Signed-off-by: Marcel Apfelbaum <mar...@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.
BTW what makes it i440fx specific? Also, what happens if you try to use it with a different machine type? > + > +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. > + > -- > 2.1.0