What is the goal of the PowerStack efforts?
What entity is funding the PowerStack initiative?
What is the current status of the PowerStack initiative?
What was the outcome of the PowerStack seminar?
What is the difference between the PowerAPI and the PowerStack efforts?
How does the PowerAPI team plan on contributing to the PowerStack initiative?
How does the EPA-JSRM team plan on contributing to the PowerStack initiative?
What are some of the potential next steps for the PowerStack initiative?

What is the goal of the PowerStack efforts?

The initial work towards the PowerStack started more than a year ago. The work arose out of the realization that there is no common consensus among the vendors/labs/academia on what software agents are needed to drive energy/power management across various layers of the system software stack and how they should interact to coordinate optimizations to power/energy at different granularities in the system. In fact, this issue has been floating around ever since the power challenges to exascale became evident. So the goal of this initiative was simple – get the community to agree upon how different software agents can interoperate with each other, without overstepping on each other’s power/energy control mechanisms. Since getting the entire community on the same page is difficult without having structured discussions and specific proposals to build on, the PowerStack core team (LLNL, TUM, Univ of Tokyo, Intel) decided to work on an initial proposal for a PowerStack strawman architecture in a small group setting to seed discussions, then bring the proposal forward to progressively broader groups for review and refinement.

What entity is funding the PowerStack initiative?

There is no centralized entity that single-handedly funds the PowerStack. The team is essentially a task-force comprising of members of academia, labs, and vendors, each specializing in some layer of the system stack. Because there is no single developer of the entire stack, it is only pragmatic for different stakeholders to design their individual products such that they are compatible with a uniform stack that drives robust energy/power management solutions.

What is the current status of the PowerStack initiative?

The steps that have been taken so far include:

  1. identify the different software actors that are involved in driving system-side efficiency
  2. identify the roles and responsibilities of each of these actors
  3. work towards prototyping how each of these actors would behave independently
  4. discuss and prototype how each of these actors would interoperate with each other
  5. prepare a strawman draft documenting this
  6. solicit feedback from some of the key HPC players to get their consensus and then decide the next steps.

For Step 3 – as a starting point – the PowerStack team chose to leverage existing open-source HPC projects like the slurm plugin, msr-safe library, and the geopm framework. Work on these projects started long before the conception of the PowerStack. Nevertheless, a conscious effort is being made to ensure that any further development on these projects is “Power Stack-aware”.

Step 4 is still a work-in-progress.

Initial strawman for Step 5 can be found here.

Step 6 took the form of an invitational PowerStack seminar, the week before ISC18 in Raitenhaslach, Germany. Due to space constraints at the venue, the attendance was limited to about 40 representatives from labs, academia, and vendors that have played a key role in designing the different layers of the HPC stack.

What was the outcome of the PowerStack seminar?

  1. the attendees came to a consensus on three key software actors that need to play a role within the PowerStack --
    1. system-wide manager (job scheduler/ job resource mgr e.g. slurm, pbspro, alps),
    2. job-level manager (e.g. geopm, conductor),
    3. physical-node manager (e.g. libmsr, papi, nvml, x86_adapt, hdeem)

    For each of these actors, the attendees identified -- the goals, the list of monitored telemetry, the list of control knobs, and the decision/arbitration mechanisms in place.
  2. The attendees agreed upon four channels of interoperability among the actors --
    1. job scheduler <--> job-level manager
    2. job scheduler <--> physical node manager
    3. job manager <--> physical node manager
    4. job scheduler <--> site-wide policy manager

    Channel (d) was initially categorized as 'out-of-scope'. Nevertheless, the attendees felt the need to discuss this briefly during the seminar. Channels (b) and (c) was where the results of the recent global survey conducted by the EPA-JSRM team (EEHPC WG) were applied, during the seminar.

    From the global survey conducted by the EPA-JSRM team, it has been evident that -- at a higher level -- sites have separate mechanisms in place for managing nodes that were idle and those that actively serviced jobs. These correspond to Channels (b) and (c), respectively.

What is the difference between the PowerAPI and the PowerStack efforts?

The charter of the PowerAPI community is to design and develop a standardized specification that helps drive energy/power efficiency among all the layers within the HPC system stack. This specification lists multiple function definitions that can be invoked by different layers of the stack. One of the strengths of the current specification is that it is very flexible in that it enables any two actors within the stack to communicate with each other via the parameters within these functions. This drives portability among vendors investing in power management.

The charter of the PowerStack community is to design a holistic, flexible and extensible concept of a software stack ecosystem Its charter is to:

  1. identify what are the different actors within the software stack that are responsible for driving energy/power efficiency
  2. get a consensus within the community about what are the roles and responsibilities of each of these actors
  3. how can these actors collaborate with each other while implementing an end-to-end solution for system efficiency
  4. aid in software-hardware co-design and engineering that is compatible with the stack.

Input from the PowerAPI + PowerStack members:
PowerAPI is a specification that allows applications, system software, and tools to have a portable, hardware/vendor-agnostic interface to the power/energy monitoring and management capabilities of a system. HPC Power Stack is a stack of hierarchical software and firmware components that optimize system-level power/energy consumption through coordinated optimization of power/energy at different granularities in the system. Where suitable, the PowerStack efforts will influence and adhere to interfaces in the PowerAPI specification for information exchange between components.

Example of a use-case:
Assume there exists a system with compute nodes that expose power capping knobs to the software stack. Assume a site policy where user-jobs are required to execute under a predetermined power budget.

The PowerAPI spec provides specific function calls that can be used to implement solutions where either the job scheduler or a job runtime or both could access the hardware knobs for enforcing the power budget. Since the actual access to the knobs would vary from one vendor to another, the PowerAPI’s plugin-in interface enables the job scheduler and a job runtime to remain oblivious of the underlying implementation.

The PowerStack effort, on the other hand, takes the approach of first getting the community to come to a consensus on – Whose responsibility is it to access the hardware knobs, in the first place? The job-scheduler, or a user-level runtime? One of the strengths of a job scheduler is that it is aware of the site-wide power policy and the status of the power consumption of the entire system. It is, however, not aware of the specific design of the jobs and its power profile. Likewise, a job manager/runtime is aware of application phases, compute-load distribution, communication patterns, and is capable of dynamically monitoring its power profile. It is, however, not aware of the power budget it should run at to ensure system-wide efficiency. This example was discussed extensively during the PowerStack seminar. The solution that was agreed upon was that it makes sense for the job scheduler to communicate the power budget to a job-level runtime. And then, it is the responsibility of the runtime to distribute the power efficiently among the nodes servicing the job.

This is in perfect alignment with some of the lessons learned from the global survey conducted by the EPA-JSRM (EEHPC WG) team – HPC sites treat “Active node power management” quite differently from “Idle node power management”. For idle nodes, the job scheduler can take up the responsibility of enforcing power caps. For nodes actively servicing jobs, the job scheduler should be capable of handing over the power capping responsibility to a job-level agent.

How does the PowerAPI team plan on contributing to

the PowerStack initiative?</a> From the PowerAPI spec – “PowerAPI provides multiple levels of abstractions to satisfy the requirements of multiple types of users”. In accordance with this, the team is willing to work with PowerStack on any and all areas where the PowerAPI function set is found insufficient. During the last two meetings, members of the PowerAPI team observed that there is a need for improving the “job-scheduler <–> user application interface” within the PowerAPI spec. To ensure that the spec does not become incompatible with the design of any of the existing power-aware job schedulers (or workload managers), it is important to include the vendors into this discussion. As one of the next steps, the PowerAPI team is interested in contributing towards a PowerStack working group (see below) that focuses on the “job-scheduler <–> job-level manager” interoperability.

How does the EPA-JSRM team plan on contributing to the PowerStack initiative?

The EPA-JSRM is in a strong position to share lessons learned from their past survey of multiple HPC sites that are actively investing in energy- and power-aware job scheduling and resource management. During the last two meetings, the EPA-JSRM team expressed interest in helping the PowerStack community by contributing some bandwidth towards designing bi-directional communication mechanisms between job schedulers and the job-level manager.

What are some of the potential next steps for the PowerStack initiative?

Towards the end of the PowerStack seminar, the attendees expressed interest in contributing towards specific working groups that focus on a specific portion of the stack. If there is enough interest, one direction we can take – as a community – is to have topic-based working groups that meet periodically to make progress on their assigned tasks.

Some candidate topics include: