Research topic and goals
This project focuses on challenges posed by the increasing complexity of HPC workflows. To cope with the ever increasing size of data and the resulting increase in the number and complexity of workflows running on Extreme-scale HPC systems, it becomes necessary to share the HPC resources across multiple scientific workflows, as is already the case on cloud infrastructures. The first goal of this research project is to investigate approaches for resource sharing and scheduling that can preserve QoS requirements of scientific workflows running concurrently on a shared HPC system, while ensuring a high resource utilization of the infrastructure. We plan to investigate the possible trade-offs including Isolation vs. performance guarantee, consolidation vs. resource utilization, and dynamicity vs. resource provisioning. Additionally, HPC workflows pose important challenges related to fault-tolerance. When a workflow fails, we need to make sure this does not affect other independent workflows. Inside a workflow when a task fails, the workflow management system should be able to reschedule the task without affecting other independent tasks.
Results for 2015/2016
Our first sub-goal consisted of investigating the potential gain of sharing resources in a “cloud way” for HPC workflows. This initial study would provide an upper bound of the gain in resource usage when independent workflow share common resources in an HPC platform. This study was mainly conducted by Nathanael Cheriere at Argonne from January to June 2016.
Results obtained using simulations with traces of real workflows showed no clear potential for resource sharing in the context of HPC workflows. Contrary to cloud workflows that can scale up and down depending on usage patterns, most HPC workflows already make the best use they can of the provided parallelism. Sharing resources presents more drawbacks than advantages and, in most cases, degrades resource utilization rather than improving it.
Results for 2016/2017
The second goal of the project will investigate mechanisms by which an HPC workflow can become fault-tolerant at task-level, so that failure of a single task has the lowest impact possible on the overall workflow. We plan to implement and demonstrate these mechanisms on real HPC workflows. This study was mainly conducted by Matthieu Dorier and Justin Wozniak from November 2016 to March 2017.
In terms of fault-tolerance, we proposed the addition of a new primitive, MPI_Comm_launch, for the MPI standard. This function enables to launch an MPI application inside another MPI application in a fault-tolerant manner. We leveraged a first implementation of MPI_Comm_launch to implement new constructs in the Swift/T language enabling a Swift workflow to be decomposed into sub-workflows. Failures in sub-workflows are reported to the parent workflow without causing it to fails, thus enabling task-level fault tolerance. We demonstrated these new features in the CODES-ESW workflow, a workflow meant for design-space exploration of network simulations. A paper with these results has been submitted to EuroMPI 2017.
Visits and meetings
Internship of Nathanael Cheriere at Argonne National Lab from January 2016 to June 2016, under the supervision of Matthieu Dorier and Rob Ross.
Impact and publications
None yet. A paper has been submitted to EuroMPI 2017.
We plan to propose our MPI_Comm_launch feature to the MPI standard committee.