High performance computing (HPC) has become an important part of the modern world: It is used almost in all of our industry today for improving products through simulating new product prototypes. In the academic world it is an essential tool for scientific research. However, systems often run far below their theoretical peak performance: In many cases only five per cent of a machine's peak performance is reached. In addition, costly components often remain idle while not being required for specific programs, as parts of HPC systems are reserved and exclusively used for the applications.

To further improve the state of the art in this research area, a project funded by the German Ministry of Education and Research (BMBF) was started in 2013. The main idea was to improve system utilization by compromising on dedicated reservations for HPC codes, and apply co-scheduling of applications instead.

As key research partners within this project, we observed a need for international discussion for finding the best solutions to this utilization issue in High Performance Computing: The approach taken by most research groups and hardware vendors is the opposite, as they try to switch off idling components, which can become quite difficult in reality. To this end, we (the editors of this book) have started to organize a workshop on Co-Scheduling in HPC, COSH, which is open to international participants and was held for the first time at the European HiPEAC conference in 2016 in Prague.

This book mainly consists of significantly extended versions of all papers submitted to this workshop. They were reviewed for a second time to ensure high scientific quality. At COSH2016 we had an invited keynote speech by Intel on recent extensions of their processors which can allow for better control of co-scheduling. We are happy to have a corresponding chapter added in this book as well as a foreword by Arndt Bode, head of one of the leading European computing centers, LRZ. Together with the project consortium leader of the abovementioned research project, André Brinkmann, we start this book with an introduction to the main challenges of Co-Scheduling as well as related research in the field.

Carsten Trinitis and Josef Weidendorfer

November 2016