Description
Building upon the success of last year, we propose a combined microconference focused on the Real-Time and Scheduler subsystems. These two areas are fundamentally intertwined and continue to drive cross-cutting changes, especially following the upstream integration of PREEMPT_RT. The Linux scheduler is central to overall system performance. Addressing the challenges of modern computingโfrom achieving low latency to maximizing high throughput across diverse topologies and workloads, and scaling from small, power-constrained devices to large-scale HPC systemsโis key to delivering the optimal user experience.
Since last yearโs microconference, progress has been made on the following topics:
- Cache aware scheduler
- Paravirt Scheduling: Framework for better physical CPU utilization
- CPU Isolation and IPI interference
- Push callback for fair scheduler
- Runtime verification
- Proxy execution
Discussions on certain topics were also carried forward at the OSPM 2026 conference.
Ideas of topics to be discussed include (but are not limited to):
- Responsiveness of fair tasks
- Improve PREEMPT_RT
- Locking and priority inversion
- Improve SCHED_DEADLINE
- CPU isolation
- New topology, including hybrid or heterogeneous system
- 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
- K Prateek Nayak
- Thomas Gleixner
- John Stulz
- Sebastian Andrzej Siewior
- Shrikanth Hegde
- Phil Auld
- Dhaval Giani
- Clark Williams
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Mr Felix Moessbauer (Siemens AG), Mr Florian Bezdeka (Siemens AG)
Realtimers know: Resource configuration for RT enabled systems is key. RT applications rely on a proper system configuration and expect this configuration to stay unmodified as long as the application is alive.
As it turned out, Linux might silently reconfigure IRQ affinities of network adapters in a way that violates the expected system configuration. While we run into this kind of problem...
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Ricardo Neri (Intel Corporation)
During OSPM 2026, there was an agreement to stop requiring schedutil to enable EAS on x86 platforms, which implies EAS may soon be active by default on these systems.
Energy-Aware Scheduling (EAS) places tasks by comparing estimated energy costs across performance domains, directing light tasks to power-efficient cores on asymmetric systems. The known trade-off is that EAS packing...
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Prateek Nayak (AMD Inc.)
As CPU counts grow, Linux scheduler scalability suffers from contention on global cpumasks โ frequent atomic updates to shared cachelines become a measurable bottleneck on large core-count systems.
Two proposals address this: Steve Sistare's sparsmask, which distributes a cpumask across multiple cachelines to reduce contention [1], and Peter Zijlstra's sbm (sparse bitmap) [2], a simpler,...
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Richard Joseph Buturla (IBM)
A task running in a vCPU may be holding a spinlock when it gets preempted by the host scheduler. Other tasks running in other vCPUs may now be blocked on that spinlock, wasting CPU time.
At IBM, we observed that under overcommit, this manifests as directed yield storms and long spinlock wait times which people have tried to mitigate in many different ways including adjusting scheduler...
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Mr Qais Yousef (Google)
Following last year discussion about userspace assissted scheduling [1], schedqos utility is announced [2] and a proposal for kernel interface to help address one of the QoS issues folks see in the wild, DVFS and migration latencies, was sent also [3].
The interface proposal is a simple extension to sched_attr, but has the goal of being extensible without requiring further addition to...
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John Stultz (Google), Suleiman <> Souhlal (Google)
More and more weโre seeing issues around priority (sometimes called performance) inversion of SCHED_NORMAL/BATCH tasks. Particularly if any sort of constraints are put on โbackgroundโ deprioritized tasks. These background tasks will eventually grab an important lock, and then wonโt be constrained and prevented from running for some extended period of time, resulting in all the important tasks...
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Mr Waiman Long (Red Hat)
By using the cpuset isolated partition functionality in the Linux
kernel, users are now able to change the set of "isolcpus[=domain]"
HK_TYPE_DOMAIN housekeeping CPUs at runtime. This feature is used by
some Kubernetes based container orchestration platforms to enable the
creation of containers running latency sensitive workloads like DPDK.Domain isolation by itself doesn't provide...
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Vincent Guittot (Linaro)
Recent improvements have been made in tasks ordering, scheduling latency and lag of the fair/EEVDF scheduler but some issues still remain and will involve more complex mechanisms. The talk will discuss possible solutions for a number of open issues:
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How to fix the remaining out of range lag of tasks ?
How to further decrease the scheduling latency ?
How to select the best CPU to minimize...