[SeaBIOS] [Qemu-devel] [PATCH v5 for-2.3 28/28] docs: Add PXB documentation

Michael S. Tsirkin mst at redhat.com
Tue Mar 10 16:47:27 CET 2015


On Tue, Mar 10, 2015 at 05:32:14PM +0200, Marcel Apfelbaum wrote:
> Signed-off-by: Marcel Apfelbaum <marcel at 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



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