[openstack-dev] [nova][scheduler] Proposal: FairShareScheduler.

Belmiro Moreira moreira.belmiro.email.lists at gmail.com
Mon Jun 30 21:42:33 UTC 2014

Hi Eric,

In my view a "FairShareScheduler" could be a very interesting option for
private clouds that support scientific communities. Basically this is the
model used by batch systems in order to fully use the available resources.

I'm very curious about the work that you are doing.
Is it available in github?



Belmiro Moreira


Email: belmiro.moreira at cern.ch

IRC: belmoreira

On Mon, Jun 30, 2014 at 4:05 PM, Eric Frizziero <eric.frizziero at pd.infn.it>

> Hi All,
> we have analyzed the nova-scheduler component (FilterScheduler) in our
> Openstack installation used by some scientific teams.
> In our scenario, the cloud resources need to be distributed among the
> teams by considering the predefined share (e.g. quota) assigned to each
> team, the portion of the resources currently used and the resources they
> have already consumed.
> We have observed that:
> 1) User requests are sequentially processed (FIFO scheduling), i.e.
> FilterScheduler doesn't provide any dynamic priority algorithm;
> 2) User requests that cannot be satisfied (e.g. if resources are not
> available) fail and will be lost, i.e. on that scenario nova-scheduler
> doesn't provide any queuing of the requests;
> 3) OpenStack simply provides a static partitioning of resources among
> various projects / teams (use of quotas). If project/team 1 in a period is
> systematically underutilizing its quota and the project/team 2 instead is
> systematically saturating its quota, the only solution to give more
> resource to project/team 2 is a manual change (to be done by the admin) to
> the related quotas.
> The need to find a better approach to enable a more effective scheduling
> in Openstack becomes more and more evident when the number of the user
> requests to be handled increases significantly. This is a well known
> problem which has already been solved in the past for the Batch Systems.
> In order to solve those issues in our usage scenario of Openstack, we have
> developed a prototype of a pluggable scheduler, named FairShareScheduler,
> with the objective to extend the existing OpenStack scheduler
> (FilterScheduler) by integrating a (batch like) dynamic priority algorithm.
> The architecture of the FairShareScheduler is explicitly designed to
> provide a high scalability level. To all user requests will be assigned a
> priority value calculated by considering the share allocated to the user by
> the administrator and the evaluation of the effective resource usage
> consumed in the recent past. All requests will be inserted in a priority
> queue, and processed in parallel by a configurable pool of workers without
> interfering with the priority order. Moreover all significant information
> (e.g. priority queue) will be stored in a persistence layer in order to
> provide a fault tolerance mechanism while a proper logging system will
> annotate all relevant events, useful for auditing processing.
> In more detail, some features of the FairshareScheduler are:
> a) It assigns dynamically the proper priority to every new user requests;
> b) The priority of the queued requests will be recalculated periodically
> using the fairshare algorithm. This feature guarantees the usage of the
> cloud resources is distributed among users and groups by considering the
> portion of the cloud resources allocated to them (i.e. share) and the
> resources already consumed;
> c) all user requests will be inserted in a (persistent) priority queue and
> then processed asynchronously by the dedicated process (filtering +
> weighting phase) when compute resources are available;
> d) From the client point of view the queued requests remain in
> “Scheduling” state till the compute resources are available. No new states
> added: this prevents any possible interaction issue with the Openstack
> clients;
> e) User requests are dequeued by a pool of WorkerThreads (configurable),
> i.e. no sequential processing of the requests;
> f) The failed requests at filtering + weighting phase may be inserted
> again in the queue for n-times (configurable).
> We have integrated the FairShareScheduler in our Openstack installation
> (release "HAVANA"). We're now working to adapt the FairShareScheduler to
> the new release "IceHouse".
> Does anyone have experiences in those issues found in our cloud scenario?
> Could the FairShareScheduler be useful for the Openstack community?
> In that case, we'll be happy to share our work.
> Any feedback/comment is welcome!
> Cheers,
> Eric.
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