Conveners
Scheduler and Real-Time MC
- Juri Lelli (Red Hat)
- Steven Rostedt
- Vincent Guittot (Linaro)
- Dhaval Giani
- Phil Auld (Red Hat)
Description
For Linux Plumber 2025, we propose a joint microconference for Real Time and Scheduler as in the past. These two areas have always been tightly linked and continue to generate cross functional changes especially after PREEMPT_RT has been merged. The scheduler is at the core of Linux performance; With different topologies and workloads, giving the user the best experience possible is challenging, from low latency to high throughput and from small power-constrained devices to HPC.
Since last yearโs micro conference, progress has been made on the following topics:
- Progress on proxy execution
- https://lore.kernel.org/all/20241011232525.2513424-1-jstultz@google.com/
- https://lore.kernel.org/all/20250602221004.3837674-1-jstultz@google.com/
- Defer throttle when task exits to user
- https://lore.kernel.org/all/20250520104110.3673059-1-ziqianlu@bytedance.com/
- The EEVDF scheduler responsiveness
- https://lore.kernel.org/all/20250418151225.3006867-1-vincent.guittot@linaro.org/
- https://lore.kernel.org/all/20250209235204.110989-1-qyousef@layalina.io/
Some topics also continued to be discussed at the OSPM conference: http://retis.sssup.it/ospm-summit/
Ideas of topics to be discussed include (but are not limited to):
- Improve responsiveness of fair tasks
- Improvements on EEVDF
- Adding more usages of push callback
- Improve PREEMPT_RT
- Defer throttle to user space
- IPI impact
- Improve Locking and priority inversion
- Proxy execution
- Impact of new topology, including hybrid or heterogeneous system
-Taking into account task profile
- Improvements on SCHED_DEADLINE and DL server
- Tooling for debugging low latency analysis
This is not an exhaustive list. We welcome all proposals related to process scheduling. The goal is to discuss open problems, preferably with patch set submissions already being discussed on the mailing list. Presentations are meant to be limited to 2 or 3 slides intended to seed a discussion and debate - allowing for high bandwidth discussion with key stakeholders in the same room.
Key attendees:
- Ingo Molnar
- Peter Zijlstra
- Juri Lelli
- Vincent Guittot
- Dietmar Eggemann
- Steven Rostedt
- Ben Segall
- Mel Gorman
- Valentin Schneider
- Thomas Gleixner
- John Stulz
- Sebastian Andrzej Siewior
- K Prateek Nayak
- Shrikanth Hegde
- Phil Auld
- Dhaval Giani
- Clark Williams
Scheduler Micro conference Proposal
Title:
Cache Aware Scheduling
Presenters:
Tim Chen (tim.c.chen@linux.intel.com)
Chen Yu (yu.c.chen@intel.com)
We have proposed RFC patch series that implemented cache aware scheduling.
The primary motivation is to keep threads sharing data together in the
same last level cache domain, to reduce cache bouncing.
We'll like community feedback...
The Binder driver is a lightweight IPC that serves as the communication backbone between processes in Android. It implements a very peculiar Priority Inheritance model that has been rejected upstream. This presentation re-examines this design and presents a few upstream-friendly alternatives to the current model.
The wakeup path and the periodic load balance donโt cover all cases where weโd like to migrate a task on another CPU for the fair scheduling class. There are situations where weโd like to push tasks in a similar way than the wake up one. The EAS is one user which would benefit from a push mechanism as it disables periodic load balance but wants to migrate tasks more often than at wakeup. Non...
During the discussion at OSPM โ25, the idea of using push-based load balancing as an alternate to idle and newidle balance was proposed. A prototype [1] was sent soon after OSPM to gather feedback from the community.
During the review, Peter mentioned optimizing the global nohz idle tracking to be reduced to per-LLC tracking to reduce the cost of access and update to this shared data being...
With the ongoing work on RV and the deadline scheduler, coupled with timed automata, we introduced a practical way to validate timing properties in the kernel.
Now we can have models guaranteeing that tasks are throttled when consuming their runtime and don't miss their deadline.
The few models for the deadline scheduler are barely scratching the surface of what could be done to validate...
CPU Isolation enables a system administrator to shield a subset of CPUs from
most kernel interference, but not all of it. Activity on the housekeeping CPUs
can still trigger IPIs targeting isolated CPUs, which defeats the requested
isolation.
At Red Hat, we've mostly observed IPIs caused by instruction patching
(e.g. static key updates) and TLB flushes (e.g. due to vmap'd stacks...
In para-virtualized environment, vCPU overcommit is a common configuration which helps customer to make better use of CPU resources since not all VMs would be active at the same time and hence underlying hypervisor will be able to meet the CPU demand and workloads running on VMs can benefit from the extra resource.
Acronyms:
vCPU - virtual CPU - CPU in VM
pCPU - physical CPU - CPU...