PCI workaround - Revision history

Sst-ska at 08:42, 1 July 2024

2024-07-01T08:42:06Z

← Older revision		Revision as of 10:42, 1 July 2024
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	[[Category: CLI]]		[[Category: CLI]]
			[[Category: Troubleshooting]]

Sst-asi at 09:37, 27 May 2022

2022-05-27T09:37:41Z

← Older revision		Revision as of 11:37, 27 May 2022
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	The property can be set during the initial upload of the image. Here is an example:		The property can be set during the initial upload of the image. Here is an example:
	<~~source~~ lang='bash'>		<syntaxhighlight lang='bash'>
	openstack image create \		openstack image create \
	--disk-format raw \		--disk-format raw \
Line 25:		Line 25:
	--property hw_machine_type=pc \		--property hw_machine_type=pc \
	"CentOS 7.6 (1901) i440fx"		"CentOS 7.6 (1901) i440fx"
	</~~source~~>		</syntaxhighlight>

	After creating the image, we can query the properties:		After creating the image, we can query the properties:
	<~~source~~ lang='bash'>		<syntaxhighlight lang='bash'>
	openstack image show \		openstack image show \
	--column properties \		--column properties \
	--format value \		--format value \
	'a416afda-3024-4404-aec3-193c210eb954'		'a416afda-3024-4404-aec3-193c210eb954'
	</~~source~~>		</syntaxhighlight>
	<~~source~~ lang='text'>		<syntaxhighlight lang='text'>
	hw_machine_type='pc', hw_qemu_guest_agent='yes', os_distro='centos', os_require_quiesce='yes', os_type='linux'		hw_machine_type='pc', hw_qemu_guest_agent='yes', os_distro='centos', os_require_quiesce='yes', os_type='linux'
	</~~source~~>		</syntaxhighlight>

	Note: It is possible to rebuild an existing VM on such an image to convert it's machine type. However, depending on the Operating System in question, this might well prevent the VM from booting because of the changes PCI layout.		Note: It is possible to rebuild an existing VM on such an image to convert it's machine type. However, depending on the Operating System in question, this might well prevent the VM from booting because of the changes PCI layout.
Line 44:		Line 44:

	To rebuild a VM, run a command similar to the below example. Note: rebuilding a VM will also restart the VM.		To rebuild a VM, run a command similar to the below example. Note: rebuilding a VM will also restart the VM.
	<~~source~~ lang='bash'>		<syntaxhighlight lang='bash'>
	image_id=b72d596f-12af-4ee3-9902-a2afbdfbf4c1		image_id=b72d596f-12af-4ee3-9902-a2afbdfbf4c1
	vm_id=e3eeb7c2-0bf1-492d-a6d5-8be3b3d30ea1		vm_id=e3eeb7c2-0bf1-492d-a6d5-8be3b3d30ea1
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	--image ${image_id} \		--image ${image_id} \
	${vm_id}		${vm_id}
	</~~source~~>		</syntaxhighlight>

	After this, the VM will have exactly one spare PCI slot.		After this, the VM will have exactly one spare PCI slot.

	[[Category: CLI]]		[[Category: CLI]]

Sst-asi at 08:42, 27 May 2022

2022-05-27T08:42:55Z

← Older revision		Revision as of 10:42, 27 May 2022
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	After this, the VM will have exactly one spare PCI slot.		After this, the VM will have exactly one spare PCI slot.

	~~[[Category: OpenStack]]~~
	[[Category: CLI]]		[[Category: CLI]]
	~~[[Category: Documentation]]~~

Sst-asi: Created page with "= Overview = In OpenStack Ocata, VMs of QEMU machine type `q35` only have a single spare PCI port. This allows to hot-plug a single PCI device only. Typical devices..."

2022-05-27T08:40:31Z

Created page with "= Overview = In OpenStack Ocata, VMs of QEMU machine type <code>q35</code> only have a single spare PCI port. This allows to hot-plug a single PCI device only. Typical devices..."

New page

= Overview =
In OpenStack Ocata, VMs of QEMU machine type <code>q35</code> only have a single spare PCI port. This allows to hot-plug a single PCI device only. Typical devices added to a VM are an additional volume or an additional network interface. Adding more than one such device after creating the VM, results in an error message. This page describes two work arounds for the problem.

= Solution 1: Change machine type =
The image property <code>hw_machine_type=pc</code> defines the QEMU machine type of the VMs created from this image. If no machine type is set, then the <code>q35</code> machine type is used. This is the prefered machine type because it can take advantage of modern virtualization technologies. It does, however, present the problem described at the top of this page.

A possible work around is to instruct OpenStack to create VMs of the machine type <code>pc-i440fx</code>. This is a legacy type which lacks some features and performance when compare to the more modern <code>q35</code>. However, it allows to hot-plug up to 31 PCI devices after VM creation.

If this solution is chose, we recommend creating a separate VM image and only building select VMs from this type while defaulting to an image which uses <code>q35</code>.

The property can be set during the initial upload of the image. Here is an example:
<source lang='bash'>
openstack image create \
--disk-format raw \
--min-ram 1 \
--file $(realpath ./scratch/CentOS-7-x86_64-GenericCloud-1901.raw) \
--protected \
--public \
--project openstack \
--project-domain default \
--property hw_qemu_guest_agent=yes \
--property os_require_quiesce=yes \
--property os_type=linux \
--property os_distro=centos \
--property hw_machine_type=pc \
"CentOS 7.6 (1901) i440fx"
</source>

After creating the image, we can query the properties:
<source lang='bash'>
openstack image show \
--column properties \
--format value \
'a416afda-3024-4404-aec3-193c210eb954'
</source>
<source lang='text'>
hw_machine_type='pc', hw_qemu_guest_agent='yes', os_distro='centos', os_require_quiesce='yes', os_type='linux'
</source>

Note: It is possible to rebuild an existing VM on such an image to convert it's machine type. However, depending on the Operating System in question, this might well prevent the VM from booting because of the changes PCI layout.

= Solution 2: Rebuild the VM =
On initial creation, a VM of the default machine type <code>q35</code> has one spare PCI slot. When adding a device to the VM after it's initial creation, this slot gets used up. Howerver, if we rebuild the VM after adding a device, a new spare PCI slot is added. This allows us to add yet another device. This process can be repeated many times.

To rebuild a VM, run a command similar to the below example. Note: rebuilding a VM will also restart the VM.
<source lang='bash'>
image_id=b72d596f-12af-4ee3-9902-a2afbdfbf4c1
vm_id=e3eeb7c2-0bf1-492d-a6d5-8be3b3d30ea1

openstack server rebuild \
--image ${image_id} \
${vm_id}
</source>

After this, the VM will have exactly one spare PCI slot.

[[Category: OpenStack]]
[[Category: CLI]]
[[Category: Documentation]]

PCI workaround - Revision history

Sst-ska at 08:42, 1 July 2024

Sst-asi at 09:37, 27 May 2022

Sst-asi at 08:42, 27 May 2022

Sst-asi: Created page with "= Overview = In OpenStack Ocata, VMs of QEMU machine type q35 only have a single spare PCI port. This allows to hot-plug a single PCI device only. Typical devices..."

Sst-asi: Created page with "= Overview = In OpenStack Ocata, VMs of QEMU machine type `q35` only have a single spare PCI port. This allows to hot-plug a single PCI device only. Typical devices..."