Hi Shaohe,
I have responded in the Etherpad. The Cyborg/Nova scheduling spec
details the 4 types of user requests
<https://git.openstack.org/cgit/openstack/cyborg/tree/doc/specs/rocky/cyborg-nova-sched.rst?h=refs/changes/17/554717/1#n136>.
I believe you are looking for more details on what the RC names, traits
and flavors will look like. I will add that to the spec itself.
Thanks,
Sundar
On 3/28/2018 2:10 AM, 少合冯 wrote:
I have summarize some scenarios for fpga devices request.
https://etherpad.openstack.org/p/cyborg-fpga-request-scenarios
Please add more more scenarios to find out the exceptions that
placement can not satisfy the filter and weight.
IMOH, I refer placementto do filter and weight. If we have to let
cyborg do filter and weight. Nova scheduler just need call cyborg
once for all host weight though we do the weigh one by one.
2018-03-23 12:27 GMT+08:00 Nadathur, Sundar <sundar.nadat...@intel.com
<mailto:sundar.nadat...@intel.com>>:
Hi all,
There seems to be a possibility of a race condition in the
Cyborg/Nova flow. Apologies for missing this earlier. (You can
refer to the proposed Cyborg/Nova spec
<https://review.openstack.org/#/c/554717/1/doc/specs/rocky/cyborg-nova-sched.rst>
for details.)
Consider the scenario where the flavor specifies a resource class
for a device type, and also specifies a function (e.g. encrypt) in
the extra specs. The Nova scheduler would only track the device
type as a resource, and Cyborg needs to track the availability of
functions. Further, to keep it simple, say all the functions exist
all the time (no reprogramming involved).
To recap, here is the scheduler flow for this case:
* A request spec with a flavor comes to Nova
conductor/scheduler. The flavor has a device type as a
resource class, and a function in the extra specs.
* Placement API returns the list of RPs (compute nodes) which
contain the requested device types (but not necessarily the
function).
* Cyborg will provide a custom filter which queries Cyborg DB.
This needs to check which hosts contain the needed function,
and filter out the rest.
* The scheduler selects one node from the filtered list, and the
request goes to the compute node.
For the filter to work, the Cyborg DB needs to maintain a table
with triples of (host, function type, #free units). The filter
checks if a given host has one or more free units of the requested
function type. But, to keep the # free units up to date, Cyborg on
the selected compute node needs to notify the Cyborg API to
decrement the #free units when an instance is spawned, and to
increment them when resources are released.
Therein lies the catch: this loop from the compute node to
controller is susceptible to race conditions. For example, if two
simultaneous requests each ask for function A, and there is only
one unit of that available, the Cyborg filter will approve both,
both may land on the same host, and one will fail. This is because
Cyborg on the controller does not decrement resource usage due to
one request before processing the next request.
This is similar to this previous Nova scheduling issue
<https://specs.openstack.org/openstack/nova-specs/specs/pike/implemented/placement-claims.html>.
That was solved by having the scheduler claim a resource in
Placement for the selected node. I don't see an analog for Cyborg,
since it would not know which node is selected.
Thanks in advance for suggestions and solutions.
Regards,
Sundar
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