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

[Marcel Apfelbaum <marcel@redhat.com>]

On 03/16/2015 05:28 PM, Michael S. Tsirkin wrote:
> On Mon, Mar 16, 2015 at 02:16:40PM +0200, Marcel Apfelbaum wrote:
>> On 03/10/2015 07:42 PM, Michael S. Tsirkin wrote:
>>> On Tue, Mar 10, 2015 at 06:21:14PM +0200, Marcel Apfelbaum wrote:
>>>> 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
>>>
>>> In fact it won't work at all. Need to think about it,
>>> maybe we can make it work more generally.
>>> For CRS, should be possible to emit for q35 too?
>> We can make it work, but not on the scope of this series.
>> However, I'll add a IHostBridgeSnoop interface that will
>> make the device work only with associated bus and
>> this will make it less general.
>>
>> Thanks,
>> Marcel
>
> OK, this works too. Do you mean PCIHostBridgeSnoop?
Sure.

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