Noisy Neighbor Strategy

https://blueprints.launchpad.net/watcher/+spec/noisy-neighbor-strategy

This spec describes a new strategy that identifies and migrates a Noisy Neighbor, which is a lower priority VM that negatively affects Last Level Cache (LLC) of a higher priority VM when located on the same host.

Problem description

Noisy neighbor is a big problem in multi-tenant clouds. Some lower priority VMs can negatively affect performance on higher priority VMs by monopolizing CPU, I/O, and network bandwidth. There are already strategies to cover some of them like CPU utilization as well as algorithm using a threshold for cache occupancy as an indicator to identify a noisy neighbor. These algorithms are too simple and do not take into consideration the interaction between VMs including the performance impact if any as well as the VMs’ relative priority to each other. For example a VM could use 50% cache occupancy and it could be fine. It all depends on the VM’s priority. This algortihm utilizes IPC, LLC and VMs’ relative priorities.

LLC(Last Level Cache), or L3 cache in X86, is critical and limit system level resource shared by all apps or VMs on the node. If one VM occupy most of L3 cache, other VMs on the node likely starve without enough L3 cache thus poor performance.

Use Cases

As an openstack operator, I need to find noisy neighbor VMs that affect my high priority VMs, and migrate them to another node that has no noisy negihbor issues.

Proposed change

  • Add one new goal - “Noisy Neighbor migration”

  • Extend base strategy classes to add one new strategy - “Noisy Neighbor solution”

  • Use Ceilometer client to get following metrics for detecting LLC noisy neighbor:

    • cpu_l3_cache – LLC occupancy of a VM

  • Algorithm to detect Noisy Neighbor:

    • Monitor L3 cache of all VMs in order of their “watcher-priority”, that is set in VM metadata. Example: L3 cache of VM with watcher-priority as “1” will be monitored before VM with watcher-priority as “8”.

    • If L3 cache of a VM goes down by more than the threshold, mark it as high priority. Then start monitoring L3 cache of VMs in reverse order of their “watcher-priority”

    • If L3 cache of a VM (VMs to be searched in reverse order of “watcher-priority”) increases by the threshold, then the VM is a noisy neighbor.

    • Look for a node with no Noisy Neighbor issue and migrate the noisy VM there.

Alternatives

None

Data model impact

None

REST API impact

None

Security impact

None

Notifications impact

None

Other end user impact

None

Performance Impact

Querying metrics will probably cause small performance drop when running the strategy.

Other deployer impact

To enable LLC metric, latest Intel server with CMT support is required. Also collectd is required to gather LLC metric data.

Developer impact

None

Implementation

Assignee(s)

Primary assignee:

<prudhvi-rao-shedimbi>

Work Items

  1. Define proper threshold for IPC and LLC

  2. Write the execute function to locate the noisy neighbor

  3. Choose target node for live migration.

Testing

Unit and functional test are needed.

Documentation Impact

Add docs on how to use this strategy.

History

None