[openstack-dev] [Nova] [Cyborg] Tracking multiple functions

Nadathur, Sundar sundar.nadathur at intel.com
Fri Mar 2 14:00:23 UTC 2018

Hello Nova team,
    During the Cyborg discussion at Rocky PTG, we proposed a flow for FPGAs wherein the request spec asks for a device type as a resource class, and optionally a function (such as encryption) in the extra specs. This does not seem to work well for the usage model that I'll describe below.

An FPGA device may implement more than one function. For example, it may implement both compression and encryption. Say a cluster has 10 devices of device type X, and each of them is programmed to offer 2 instances of function A and 4 instances of function B. More specifically, the device may implement 6 PCI functions, with 2 of them tied to function A, and the other 4 tied to function B. So, we could have 6 separate instances accessing functions on the same device.

In the current flow, the device type X is modeled as a resource class, so Placement will count how many of them are in use. A flavor for 'RC device-type-X + function A' will consume one instance of the RC device-type-X.  But this is not right because this precludes other functions on the same device instance from getting used.

One way to solve this is to declare functions A and B as resource classes themselves and have the flavor request the function RC. Placement will then correctly count the function instances. However, there is still a problem: if the requested function A is not available, Placement will return an empty list of RPs, but we need some way to reprogram some device to create an instance of function A.


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