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

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.

> 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.

> 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,...

> 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'

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.