Re: [libvirt] [RFC PATCH] support multifunction PCI device

On Wed, May 11, 2011 at 10:30:43AM +0800, Wen Congyang wrote: > At 05/10/2011 06:00 PM, Daniel P. Berrange Write: >> On Tue, May 10, 2011 at 02:00:17PM +0800, Wen Congyang wrote: >>> We want to use more than 200+ device. Libvirt does not use multi >>> function PCI device and PCI-to-PCI bridge. So we can not use more >>> than 200+ device if it's a PCI device or it's controller is a PCI >>> device. >> >> IMHO using multi function support is a dead end, because it >> makes hotplug completely unusable and is not even possible >> for most PCI devices. The way we want to raise the device >> limit is >> >> a. Supporting multiple PCI domains (multiple PCI root complexes) > > IIUC, qemu do not support multiple PCI domains now. There are people who are working on making that supported in KVM real soon.

>> b. Adding PCI bridges > > I do not know whether qemu supports it. I find hw/pci_bridge.c in qemu's source, > so qemu may support it. I will confirm it. I'm told this is already supported, but I've not tested it myself.

>> c. A virtio-scsi controller to allow > 1 virtio disk per PCI device > > Hmm, do you mean this: > -device virtio-blk-pci,ports=4,drive0=hda,drive1=hdb,drive2=hdc,... No it is actually going to be a new device type, and I'm expecting it will work very like the LSI scsi does in terms of device setup. eg create a controller device, and then create devices for each drive. -device virtio-scsi-pci,id=vscsi1 -drive file=/some/disk,id=vscsi1.1 -device virtio-blk-pci,bus=vscsi1,drive=vscsi1.1 -drive file=/some/disk,id=vscsi1.2 -device virtio-blk-pci,bus=vscsi1,drive=vscsi1.2 -drive file=/some/disk,id=vscsi1.2 -device virtio-blk-pci,bus=vscsi1,drive=vscsi1.2 >> any of those will dramatically increase the number of devices >> we can use without the horrible hotplug problems that multifunction >> introduces. >> >>> This patch adds the support of multi function PCI device. It >>> does not support to hot plug/unplug multi function PCI device. >>> >>> TODO: >>> 1. support to hot plug multi function PCI device >>> We only can hot plug one device at one time. I think we should >>> introduce another command 'virsh attach-devices XXX' to support >>> hot plug more than one device at one time? >> >> Since you can't do practical hotplug of multifunction devices at the >> QEMU layer at all, there's nothing useful we can do at libvirt either. > > We can hotplug multifunction PCI devices like this: > 1. Before hot pluging, > # lspci > 00:00.0 Host bridge: Intel Corporation 440FX - 82441FX PMC [Natoma] (rev 02) > 00:01.0 ISA bridge: Intel Corporation 82371SB PIIX3 ISA [Natoma/Triton II] > 00:01.1 IDE interface: Intel Corporation 82371SB PIIX3 IDE [Natoma/Triton II] > 00:01.2 USB Controller: Intel Corporation 82371SB PIIX3 USB [Natoma/Triton II] (rev 01) > 00:01.3 Bridge: Intel Corporation 82371AB/EB/MB PIIX4 ACPI (rev 03) > 00:02.0 VGA compatible controller: Cirrus Logic GD 5446 > 00:03.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+ (rev 20) > 00:04.0 RAM memory: Red Hat, Inc Virtio memory balloon > 00:05.0 SCSI storage controller: LSI Logic / Symbios Logic 53c895a > > 2. hot plug multi function PCI devices: > # virsh qemu-monitor-command vm1 --hmp 'device_add lsi,id=scsi2,bus=pci.0,addr=0x06.0x07' > # virsh qemu-monitor-command vm1 --hmp 'device_add lsi,id=scsi3,bus=pci.0,addr=0x06.0x06' > # virsh qemu-monitor-command vm1 --hmp 'device_add lsi,id=scsi4,bus=pci.0,addr=0x06.0x05' > # virsh qemu-monitor-command vm1 --hmp 'device_add lsi,id=scsi5,bus=pci.0,addr=0x06.0x04' > # virsh qemu-monitor-command vm1 --hmp 'device_add lsi,id=scsi6,bus=pci.0,addr=0x06.0x03' > # virsh qemu-monitor-command vm1 --hmp 'device_add lsi,id=scsi7,bus=pci.0,addr=0x06.0x02' > # virsh qemu-monitor-command vm1 --hmp 'device_add lsi,id=scsi8,bus=pci.0,addr=0x06.0x01' > # virsh qemu-monitor-command vm1 --hmp 'device_add lsi,id=scsi9,multifunction=on,bus=pci.0,addr=0x06.0x00' Hmm, that's kinda wierd & i'm suprised it works, particularly for LSI since I thought guest drivers would need support for multifunction too.

> > 3. After hot plug multi function PCI devices: > # lspci > 00:00.0 Host bridge: Intel Corporation 440FX - 82441FX PMC [Natoma] (rev 02) > 00:01.0 ISA bridge: Intel Corporation 82371SB PIIX3 ISA [Natoma/Triton II] > 00:01.1 IDE interface: Intel Corporation 82371SB PIIX3 IDE [Natoma/Triton II] > 00:01.2 USB Controller: Intel Corporation 82371SB PIIX3 USB [Natoma/Triton II] (rev 01) > 00:01.3 Bridge: Intel Corporation 82371AB/EB/MB PIIX4 ACPI (rev 03) > 00:02.0 VGA compatible controller: Cirrus Logic GD 5446 > 00:03.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+ (rev 20) > 00:04.0 RAM memory: Red Hat, Inc Virtio memory balloon > 00:05.0 SCSI storage controller: LSI Logic / Symbios Logic 53c895a > 00:06.0 SCSI storage controller: LSI Logic / Symbios Logic 53c895a > 00:06.1 SCSI storage controller: LSI Logic / Symbios Logic 53c895a > 00:06.2 SCSI storage controller: LSI Logic / Symbios Logic 53c895a > 00:06.3 SCSI storage controller: LSI Logic / Symbios Logic 53c895a > 00:06.4 SCSI storage controller: LSI Logic / Symbios Logic 53c895a > 00:06.5 SCSI storage controller: LSI Logic / Symbios Logic 53c895a > 00:06.6 SCSI storage controller: LSI Logic / Symbios Logic 53c895a > 00:06.7 SCSI storage controller: LSI Logic / Symbios Logic 53c895a > > >> >>> >>> 2. support to hot unplug multi function PCI device >>> hot unpluging multi function PCI device meas that all the other >>> devices on the same slot will be hot unpluged. So we should do >>> some cleanup and remove the other devices too. If the other >>> device on the same slot does not support hot unpluged, or it is a >>> a controller and some other devices still use this controller, >>> I think we should refuse to hot unplug this mutlti function PCI >>> device. >> >> IMHO these kind of restrictions will make life really unpleasant >> for applications and are a reason we should *not* support the >> multifunction code. Instead we should focus on one of the other >> 3 options I mention above. > > Yes, there's too many restrictions about hot plug/unplug multifunction > PCI devices. Regards, Daniel