Sep 12 – 14, 2022
Europe/Dublin timezone

OS Scheduling with Nest: Keeping Tasks Close Together on Warm Cores

Sep 12, 2022, 12:45 PM
"Lansdowne" (Clayton Hotel on Burlington Road)


Clayton Hotel on Burlington Road

LPC Refereed Track LPC Refereed Track


Julia Lawall (Inria)


To best support highly parallel applications, Linux's CFS scheduler tends to spread tasks across the machine on task creation and wakeup. It has been observed, however, that in a server environment, such a strategy leads to tasks being unnecessarily placed on long-idle cores that are running at lower frequencies, reducing performance, and to tasks being unnecessarily distributed across sockets, consuming more energy. In this talk, we propose to exploit the principle of core reuse, by constructing a nest of cores to be used in priority for task scheduling, thus obtaining higher frequencies and using fewer sockets. We implement the Nest scheduler in the Linux kernel. While performance and energy usage are comparable to CFS for highly parallel applications, for a range of applications using fewer tasks than cores, Nest improves performance 10%-2x and can reduce energy usage.

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Primary author

Julia Lawall (Inria)


Himadri Chhaya-Shailesh (Inria) Jean-Pierre Lozi (Oracle Labs) Baptiste Lepers (University of Sydney) Willy Zwaenepoel (Uniervsity of Syndey) Gilles Muller (Inria)

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