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

[Marcel Apfelbaum <marcel@redhat.com>]

On 03/10/2015 05:47 PM, Michael S. Tsirkin wrote:
> On Tue, Mar 10, 2015 at 05:32:14PM +0200, Marcel Apfelbaum wrote:
>> 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.
>
> BTW what makes it i440fx specific?
> Also, what happens if you try to use it
> with a different machine type?
Is is i440fx specific, please look at patch 22/28.
Also we have a specific check for i440fx, so CRS
will not be emitted for other machine types.

Thanks,
Marcel

>
>> +
>> +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