[openstack-dev] [nova][ironic] Concerns over rigid resource class-only ironic scheduling

Ed Leafe ed at leafe.com
Fri Oct 27 02:42:22 UTC 2017

On Oct 26, 2017, at 6:57 PM, Wan-yen Hsu <wanyenhsu at gmail.com> wrote:

> In Nisha's message, "capabilities" refers to "ComputeCapabilitiesFilter".   "capabilities" provides a lot of flexibility for scheduling.  It supports qualitative as well as quantitative attributes.  It supports a variety of operators such as ">=", "<", "=", etc.   For instance, with "capabilities", one can create a flavor for "GPU_Count >=2".  Quantity matters for workloads.  A workload may require at least 2GPUs or at least certain amount of SSD capacity to meet the performance requirements.   Trait will help but it only supports qualitative attributes.  Therefore, we still need "capabilities".

In your example, you would create a resource class that specifies the number of GPUs. If there is a machine with no GPU, it would be a different resource class than a machine with a GPU. Likewise, a machine with 2 GPUs would be a different class. This gives you the ability to match the request to the need. Saying you need a machine with at least 2 GPUs means that you could end up with a machine with 100 GPUs - ok, I know that's not realistic, but it illustrates my point. Each hardware combination is a separate resource class. If your workload requires 2 GPUs and SSD, there are a finite number of hardware combinations available. You pick the flavor (i.e., resource class) that matches your need.

-- Ed Leafe

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