5:29 p.m.
On Thu, Aug 18, 2016 at 09:41:59AM -0700, Neo Jia wrote:
Hi libvirt experts,
I am starting this email thread to discuss the potential solution / proposal of
integrating vGPU support into libvirt for QEMU.
Some quick background, NVIDIA is implementing a VFIO based mediated device
framework to allow people to virtualize their devices without SR-IOV, for
example NVIDIA vGPU, and Intel KVMGT. Within this framework, we are reusing the
VFIO API to process the memory / interrupt as what QEMU does today with passthru
device.
The difference here is that we are introducing a set of new sysfs file for
virtual device discovery and life cycle management due to its virtual nature.
Here is the summary of the sysfs, when they will be created and how they should
be used:
1. Discover mediated device
As part of physical device initialization process, vendor driver will register
their physical devices, which will be used to create virtual device (mediated
device, aka mdev) to the mediated framework.
Then, the sysfs file "mdev_supported_types" will be available under the
physical
device sysfs, and it will indicate the supported mdev and configuration for this
particular physical device, and the content may change dynamically based on the
system's current configurations, so libvirt needs to query this file every time
before create a mdev.
Note: different vendors might have their own specific configuration sysfs as
well, if they don't have pre-defined types.
For example, we have a NVIDIA Tesla M60 on 86:00.0 here registered, and here is
NVIDIA specific configuration on an idle system.
For example, to query the "mdev_supported_types" on this Tesla M60:
cat /sys/bus/pci/devices/0000:86:00.0/mdev_supported_types
# vgpu_type_id, vgpu_type, max_instance, num_heads, frl_config, framebuffer,
max_resolution
11 ,"GRID M60-0B", 16, 2, 45, 512M, 2560x1600
12 ,"GRID M60-0Q", 16, 2, 60, 512M, 2560x1600
13 ,"GRID M60-1B", 8, 2, 45, 1024M, 2560x1600
14 ,"GRID M60-1Q", 8, 2, 60, 1024M, 2560x1600
15 ,"GRID M60-2B", 4, 2, 45, 2048M, 2560x1600
16 ,"GRID M60-2Q", 4, 4, 60, 2048M, 2560x1600
17 ,"GRID M60-4Q", 2, 4, 60, 4096M, 3840x2160
18 ,"GRID M60-8Q", 1, 4, 60, 8192M, 3840x2160
I'm unclear on the requirements about data format for this file.
Looking at the docs:
http://www.spinics.net/lists/kvm/msg136476.html
the format is completely unspecified.
2. Create/destroy mediated device
Two sysfs files are available under the physical device sysfs path : mdev_create
and mdev_destroy
The syntax of creating a mdev is:
echo "$mdev_UUID:vendor_specific_argument_list" >
/sys/bus/pci/devices/.../mdev_create
I'm not really a fan of the idea of having to provide arbitrary vendor
specific arguments to the mdev_create call, as I don't really want to
have to create vendor specific code for each vendor's vGPU hardware in
libvirt.
What is the relationship between the mdev_supported_types data and
the vendor_specific_argument_list requirements ?
The syntax of destroying a mdev is:
echo "$mdev_UUID:vendor_specific_argument_list" >
/sys/bus/pci/devices/.../mdev_destroy
The $mdev_UUID is a unique identifier for this mdev device to be created, and it
is unique per system.
For NVIDIA vGPU, we require a vGPU type identifier (shown as vgpu_type_id in
above Tesla M60 output), and a VM UUID to be passed as
"vendor_specific_argument_list".
If there is no vendor specific arguments required, either "$mdev_UUID" or
"$mdev_UUID:" will be acceptable as input syntax for the above two commands.
This raises the question of how an application discovers what
vendor specific arguments are required or not, and what they
might mean.
To create a M60-4Q device, libvirt needs to do:
echo "$mdev_UUID:vgpu_type_id=20,vm_uuid=$VM_UUID" >
/sys/bus/pci/devices/0000\:86\:00.0/mdev_create
Overall it doesn't seem like the proposed kernel interfaces provide
enough vendor abstraction to be able to use this functionality without
having to create vendor specific code in libvirt, which is something
I want to avoid us doing.
Ignoring the details though, in terms of libvirt integration, I think I'd
see us primarily doing work in the node device APIs / XML. Specifically
for physical devices, we'd have to report whether they support the
mediated device feature and some way to enumerate the validate device
types that can be created. The node device creation API would have to
support create/deletion of the devices (mapping to mdev_create/destroy)
When configuring a guest VM, we'd use the <hostdev> XML to point to one
or more mediated devices that have been created via the node device APIs
previously. When starting the guest, we'd set those mediate devices
online.
Regards,
Daniel
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