[openstack-dev] vGPUs support for Nova - Implementation

Jay Pipes jaypipes at gmail.com
Fri Sep 29 15:16:43 UTC 2017

Hi Sahid, comments inline. :)

On 09/29/2017 04:53 AM, Sahid Orentino Ferdjaoui wrote:
> On Thu, Sep 28, 2017 at 05:06:16PM -0400, Jay Pipes wrote:
>> On 09/28/2017 11:37 AM, Sahid Orentino Ferdjaoui wrote:
>>> Please consider the support of MDEV for the /pci framework which
>>> provides support for vGPUs [0].
>>> Accordingly to the discussion [1]
>>> With this first implementation which could be used as a skeleton for
>>> implementing PCI Devices in Resource Tracker
>> I'm not entirely sure what you're referring to above as "implementing PCI
>> devices in Resource Tracker". Could you elaborate? The resource tracker
>> already embeds a PciManager object that manages PCI devices, as you know.
>> Perhaps you meant "implement PCI devices as Resource Providers"?
> A PciManager? I know that we have a field PCI_DEVICE :) - I guess a
> virt driver can return inventory with total of PCI devices. Talking
> about manager, not sure.

I'm referring to this:


The PciDevTracker class is instantiated in the resource tracker when the 
first ComputeNode object managed by the resource tracker is init'd:


On initialization, the PciDevTracker inventories the compute node's 
collection of PCI devices by grabbing a list of records from the 
pci_devices table in the cell database:


and then comparing those DB records with information the hypervisor 
returns about PCI devices:


Each hypervisor returns something different for the list of pci devices, 
as you know. For libvirt, the call that returns PCI device information 
is here:


The results of that are jammed into a "pci_passthrough_devices" key in 
the returned result of the virt driver's get_available_resource() call. 
For libvirt, that's here:


It is that piece that Eric and myself have been talking about 
standardizing into a "generic device management" interface that would 
have an update_inventory() method that accepts a ProviderTree object [1]


and would add resource providers corresponding to devices that are made 
available to guests for use.

> You still have to define "traits", basically for physical network
> devices, the users want to select device according physical network,
> to select device according the placement on host (NUMA), to select the
> device according the bandwidth capability... For GPU it's same
> story. *And I do not have mentioned devices which support virtual
> functions.*

Yes, the generic device manager would be responsible for associating 
traits to the resource providers it adds to the ProviderTree provided to 
it in the update_inventory() call.

> So that is what you plan to do for this release :) - Reasonably I
> don't think we are close to have something ready for production.

I don't disagree with you that this is a huge amount of refactoring to 
undertake over the next couple releases. :)

> Jay, I have question, Why you don't start by exposing NUMA ?

I believe you're asking here why we don't start by modeling NUMA nodes 
as child resource providers of the compute node? Instead of starting by 
modeling PCI devices as child providers of the compute node? If that's 
not what you're asking, please do clarify...

We're starting with modeling PCI devices as child providers of the 
compute node because they are easier to deal with as a whole than NUMA 
nodes and we have the potential of being able to remove the 
PciPassthroughFilter from the scheduler in Queens.

I don't see us being able to remove the NUMATopologyFilter from the 
scheduler in Queens because of the complexity involved in how coupled 
the NUMA topology resource handling is to CPU pinning, huge page 
support, and IO emulation thread pinning.

Hope that answers that question; again, lemme know if that's not the 
question you were asking! :)

>> For the record, I have zero confidence in any existing "functional" tests
>> for NUMA, SR-IOV, CPU pinning, huge pages, and the like. Unfortunately, due
>> to the fact that these features often require hardware that either the
>> upstream community CI lacks or that depends on libraries, drivers and kernel
>> versions that really aren't available to non-bleeding edge users (or users
>> with very deep pockets).
> It's good point, if you are not confidence, don't you think it's
> premature to move forward on implementing new thing without to have
> well trusted functional tests?

Completely agree with you. I would rather see functional integration 
tests that are proven to actually test these complex hardware devices 
*gating* Nova patches before adding any new functionality to Nova.

We're adding lots of functional tests of the placement and resource 
providers modeling. I could definitely use some assistance from folks 
with access to this specialized hardware to set up and maintain the CI 
systems that can provide they are actually exercising these code paths.

>>> * The Usage
>>> There are no difference between SR-IOV and MDEV, from operators point
>>> of view who knows how to expose SR-IOV devices in Nova, they already
>>> know how to expose MDEV devices (vGPUs).
>>> Operators will be able to expose MDEV devices in the same manner as
>>> they expose SR-IOV:
>>>    1/ Configure whitelist devices
>>>    ['{"vendor_id":"10de"}']
>>>    2/ Create aliases
>>>    [{"vendor_id":"10de", "name":"vGPU"}]
>>>    3/ Configure the flavor
>>>    openstack flavor set --property "pci_passthrough:alias"="vGPU:1"
>>> * Limitations
>>> The mdev does not provide 'product_id' but 'mdev_type' which should be
>>> considered to exactly identify which resource users can request e.g:
>>> nvidia-10. To provide that support we have to add a new field
>>> 'mdev_type' so aliases could be something like:
>>>    {"vendor_id":"10de", mdev_type="nvidia-10" "name":"alias-nvidia-10"}
>>>    {"vendor_id":"10de", mdev_type="nvidia-11" "name":"alias-nvidia-11"}
>>> I do have plan to add but first I need to have support from upstream
>>> to continue that work.
>> As mentioned in IRC and the previous ML discussion, my focus is on the
>> nested resource providers work and reviews, along with the other two
>> top-priority scheduler items (move operations and alternate hosts).
>> I'll do my best to look at your patch series, but please note it's lower
>> priority than a number of other items.
> No worries, the code is here, tested, fully functionnal and
> production-ready, I made effort to make it available at the very
> beginning of the release. With some good volitions we could fix any
> bugs and have support for vGPUs in Queens.

You cannot say it's tested, fully functional and production-ready until 
we see functional integration tests proving that :)

>> One thing that would be very useful, Sahid, if you could get with Eric Fried
>> (efried) on IRC and discuss with him the "generic device management" system
>> that was discussed at the PTG. It's likely that the /pci module is going to
>> be overhauled in Rocky and it would be good to have the mdev device
>> management API requirements included in that discussion.

Perhaps you missed the above part of my response. I'd like to repeat 
that it would be great to get your input on the generic device 
management ideas we've been throwing around.

All the best,

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