Real-time Linux Summit 2019: Schedule

9:00 – 9:30Opening Talk “Real-time Linux: what is, what is not and what is next!
Daniel Bristot de Oliveira, Red Hat.
9:30 – 10:15Real-time Linux in Financial Markets
Adrien Mahieux, Orness.
10:15 – 10:30Pause
10:30 – 11:15Supporting Real-Time Hardware Acceleration on Dynamically Reconfigurable
Marco Pagani, Scuola Superiore Sant’Anna – Université de Lille.
11:15 – 12:00 Real-time usage in the BeagleBone community
Drew Fustini, Foundation.
12:00 – 13:30Lunch Pause
13:30 – 14:15 Maintaining out of tree patches over the long term
Daniel Wagner, SUSE.
14:15 – 15:00Synthetic events and basic histograms
Steven Rostedt, VMware.
15:00 – 15:15 Pause
15:15 – 16:00State of the PREEMPT_RT
Sebastian Andrzej Siewior, Linutronix GmbH.
16:00 – 16:45PREEMPT RT is Upstream! Q&A Session
Thomas Gleixner, Linutronix GmbH.
16:45 – 17:00Closing

Real-time Linux – What is, what is not and what is next.

Daniel Bristot de Oliveira, Red Hat


This talk is a reflexion about the current state of the Real-time Linux, regarding the kind of determinism that is possible to obtain with Linux, and the kind of determinism that is still not possible to achieve. Knowing what is not possible is not a bad thing – rather, it opens the possibilities for the next opportunities in the development of Real-time Linux.


Daniel is a Principal Software Engineer at Red Hat, working in the real-time kernel team. He is also a researcher in the Retis Lab at the Scuola Superiore Sant’Anna (Pisa – Italy). He works in the research and development of new real-time features and runtime formal verification methods for the Linux kernel.

Real-time Linux in Financial Markets

Adrien Mahieux, Orness


Provide an insight into how Linux Realtime is used, and demystify some ideas about electronic finance. Introduction to finance and stock markets:

– What’s a stock exchange
– What strategies
– Current Status of the markets

Why RT is needed (5min)
– HFT is not what you think: front-running, moving orders
– Usage from the market: gateway & matching engine
– Usage from the client: fight against front-running

Challenges & Tools (10min)
– Work with newer hardware (processor, NICs, FPGA)
– Very custom hardware on x86 systems
– kthread stalls (rcu, rt_mutex), kernel bypass, interrupt silencing, and help from Redhat kernel engineers
– Measurements: rt_test, sys_jitter, netdata, pcm.


Before the internet was a worldwide public standard, he used to organize LAN Parties: ephemeral infrastructures for hundreds of players. Every available resource was scarce and optimized. Now in this era of opulence, he helps companies in this search of parsimony through analysis and optimization of their whole stack. This is useful for HPC (throughput) and HFT (latency).

Supporting Real-Time Hardware Acceleration on Dynamically Reconfigurable SoC FPGAs

Marco Pagani, Scuola Superiore Sant’Anna – Université de Lille


SoCs including multiple CPU tightly coupled with FPGA fabric, like the Xilinx’s Zynq and Zynq UltraScale, are popular for developing high-performance applications like computer vision and signal processing. On these platforms, software activities can be accelerated using custom hardware accelerators. Nowadays, dynamic partial reconfiguration allows virtualizing the FPGA resources to host, in time-sharing, more hardware accelerators than what statically possible. However, without a proper scheduling policy, FPGA reconfiguration may introduce unbounded delays unsuitable for real-time applications like autonomous vehicles. This talk presents FRED, a Linux based framework that enables real-time scheduling of hardware accelerators on the FPGA fabric. FRED exploits dynamic partial reconfiguration and recurrent execution to virtualize the FPGA fabric at production time in a predictable fashion.


Marco Pagani received his M.Sc. degree in Embedded Computing Systems cum Laude in 2016 jointly from Scuola Superiore Sant’Anna and the University of Pisa. He is currently pursuing the Ph.D. degree in Emerging Digital Technologies at Scuola Superiore Sant’Anna and Université de Lille. His main research interests are software support for real-time applications on heterogeneous computing platforms, real-time hardware acceleration, and real-time operating systems for embedded platforms.

Real-time usage in the BeagleBone community

Drew Fustini, Foundation


Many open-source hardware projects have been produced by the BeagleBone community that have real-time requirements.  These include motion control for CNC, laser cutting, and 3d printing. Other projects include autopilots, low latency audio processing, driving large LED displays, and high-speed data acquisition.  I’ll provide a look at projects like MachineKit (LinuxCNC fork) which migrating from Xenomai from PREEMPT_RT Kernel.


Drew Fustini is an Open Source Hardware designer at OSH Park, board member of the BeagleBoard Foundation, vice president of the Open Source Hardware Association, and maintainer of the Adafruit BeagleBone Python library

Maintaining out of tree patches over the long term

Daniel Wagner, SUSE


The PREEMPT_RT patchset is the longest existing large patchset living outside the Linux kernel. Over the years, the realtime developers had to maintain several stable kernel versions of the patchset. This talk will present the lessons learned from this experience, including workflow, tooling and release management that has proven over time to scale. The workflow deals with upstream changes and changes to the patchset itself. Now that the PREEMPT_RT patchset is about the be merged upstream, we want to share our toolset and methods with others who may be able to benefit from our experience. This talk is for people who want to maintain an external patchset with stable releases.


Daniel Wagner is a stable-rt tree maintainer and contributor to various upstream projects (preempt_rt, ConnMan, FFADO,…)

Synthetic events and basic histograms

Steven Rostedt, VMware


Synthetic events were introduced in 4.17 which allow for passing data from one trace event to another and using it to calculate deltas between fields and time stamps. This allows a user to create their own custom latency histograms or other data. In 5.0, easier access to arguments was added to kprobes. The combination allows for extracting data from the kernel and using it as part of the synthetic events and histogram logic. This talk will describe what is in the kernel today and some features that are coming in userspace tools that will make this easier to work with.


Steven Rostedt currently works for VMware in their Open Source Technology Center. He’s the maintainer of the stable releases for the Real-Time patch (PREEMPT_RT). He is also one of the original developers for the Real-Time patch. Steven is the main developer and maintainer for ftrace, the official tracer of the Linux kernel, as well as the userspace tools trace-cmd and kernelshark. He also develops (in the kernel) and make localmodconfig.

State of the PREEMPT_RT

Sebastian Andrzej Siewior, Linutronix GmbH.


The RT patch is maintained for a long time. More and more bits and pieces were merged in the upstream kernel and were removed from the RT patch since. As a result of this, the RT queue got more and more RT specific and it was harder to argue that the non-RT benefits from the change. In v5.3 upstream, the CONFIG_PREEMPT_RT option finally appeared. This talk shows what big changes occurred in the recent release and what is planned for the feature.


Sebastian maintains the PREEMPT_RT patch since around v3.8 and contributes to the upstream kernel by posting patches from the RT queue which are beneficial to the kernel without the RT patch.

[CFP] Real-Time Summit 2019 Call for Presentations

The Real-Time Summit is organized by the Linux Foundation Real-Time Linux (RTL) collaborative project. The event is intended to gather developers and users of Linux as a Real-Time Operating System. The main intent is to provide room for discussion between developers, tooling experts, and users.

The summit will take place alongside the Open Source Summit + Embedded Linux Conference Europe 2019 in Lyon, France. The summit is planned the day after the main conference, Thursday, October 31st, 2019, from 8:00 to 17:00 at the conference venue. If you are already considering your travel arrangements for the Open Source Summit + Embedded Linux Conference Europe 2019 in Lyon, France, and you have a general interest in this topic, please extend your travel by one day to be in Lyon on Thursday, 31st.

If you are interested to present, please submit a proposal [1] before September 14th, 2019, at 23:59 EST. Please provide a title, an abstract describing the proposed talk (900 characters maximum), a short biography (900 characters maximum), and describe the targeted audience (900 characters maximum). Please indicate the slot length you are aiming for: The format is a single track with presentation slots of 30, 45 or 60 minutes long. Considering that the presentation should use at most half of the slot time, leaving the rest of the slot reserved for discussion. The focus of this event is the discussion.

We are welcoming presentations from both end-users and developers, on topics covering, but not limited to:

  • Real-time Linux development
  • Real-time Linux evaluation
  • Real-time Linux use cases (Success and failures)
  • Real-time Linux tooling (tracing, configuration, …)
  • Real-time Linux academic work, already presented or under development, for direct feedback from practitioners community.

Those can cover recently available technologies, ongoing work, and new ideas.

Important Notes for Speakers:

  • All speakers are required to adhere to the Linux Foundation events’ Code of Conduct. We also highly recommend that speakers take the Linux Foundation online Inclusive Speaker Orientation Course.
  • Avoid sales or marketing pitches and discussing unlicensed or potentially closed-source technologies when preparing your proposal; these talks are almost always rejected due to the fact that they take away from the integrity of our events, and are rarely well-received by conference attendees.
  • All accepted speakers are required to submit their slides prior to the event.

Submission must be received by 11:59 pm PST on September 14th, 2019

[1] Submission page:

Important Dates:

  • CFP Close: Saturday, September 14th, 2019, 11:59PM PST
  • Speaker notification: September 21st, 2019
  • Conference: Thursday, October 31st, 2019

Questions on submitting a proposal? Email Daniel Bristot de Oliveira <>

Paper accepted at SEFM 2019

I had the paper “Efficient Formal Verification for the Linux Kernel” at the 17th International Conference on Software Engineering and Formal Methods (SEFM 2019).

It has the following abstract:

Formal verification of the Linux kernel has been receiving increasing attention in recent years, with the development of many models, from memory subsystems to the synchronization primitives of the real-time kernel. The effort in developing formal verification methods is justified considering the large code-base, the complexity in synchronization required in a monolithic kernel and the support for multiple architectures, along with the usage of Linux on critical systems, from high-frequency trading to self-driven cars. Despite recent developments in the area, none of the proposed approaches are suitable and flexible enough to be applied in an efficient way to a running kernel. Aiming to fill such a gap, this paper proposes a formal verification approach for the Linux kernel, based on automata models. It presents a method to auto-generate verification code from an automaton, which can be integrated into a module and dynamically added into the kernel for efficient on-the-fly verification of the system, using in-kernel tracing features. Finally, a set of experiments demonstrate verification of three models, along with performance analysis of the impact of the verification, in terms of latency and throughput of the system, showing the efficiency of the approach.

Sincerely, this is the paper I most enjoyed writing. It has a very easy reading and good practical results. But the best thing is that, by having my approach recognized by the formal methods community, I feel more conformable about using the word “formal“, which is a very strong word. This is one of the cherries of my Ph.D. Now it is time to work in the second cherry…. and that we are done.

I am also curious to attend the conference, the list of paper is very interesting, and I need to deeper my knowledge in the area.

Real-time Micro-conference accepted at the Linux Plumbers Conference 2019

From the announcement:

We are pleased to announce that the Real-Time Microconference has been
accepted into the 2019 Linux Plumbers Conference! The PREEMPT_RT patch
set (aka “The Real-Time Patch”) was created in 2004 in the effort to
make Linux into a hard real-time designed operating system. Over the
years much of the RT patch has made it into mainline Linux, which
includes: mutexes, lockdep, high-resolution timers, Ftrace,
RCU_PREEMPT, priority inheritance, threaded interrupts and much more.
There’s just a little left to get RT fully into mainline, and the light
at the end of the tunnel is finally in view. It is expected that the RT
patch will be in mainline within a year, which changes the topics of
discussion. Once it is in Linus’s tree, a whole new set of issues must
be handled. The focus on this year’s Plumbers events will include:

 – Real-time containers
 – Rework of softirqs (Requirement for the PREEMPT-RT merge)  [2]
 – An in-kernel view of latency [1]
 – Improvements in the locking determinism [4]
 – Advances in the RCU for reducing the per-cpu workload
 – The effects of BPF in the kernel latency
 – Core scheduling and Real-time schedulers [5]
 – Maintaining the RT stable trees [3]
 – New tools to test RT kernels [6]
 – New bootup self-tests
 – New types of failures that lockdep can detect after RT is merged

Come and join us in the discussion of making the LWN prediction of RT
coming into mainline “this year” a reality!
We hope to see you there[7]!
LPC[8] will be held in Lisbon, Portugal from Monday, September 9
through Wednesday, September 11.

[1]  Continuation of last year’s “New metrics for the PREEMPT RT”
[4] & continuation of last year’s
“SCHED_DEADLINE desiderata and slightly crazy ideas.”
[6] Continuation of last year’s discussion: “How can we catch problems that can break the PREEMPT_RT preemption model?”

Kernel Recipes 2019 Talk!

I was invited to give a talk a the Kernel Recipes Conference in Paris. So, I decided to talk about formal modeling, but in an easy way. Here is the description of the talk. I hope people enjoy it.

Formal modeling made easy

Modeling parts of Linux has become a recurring topic. For instance, the memory model, the model for PREEMPT_RT synchronization, and so on.
But the term “formal model” causes panic for most of the developers. Mainly because of the complex notations and reasoning that involves formal languages. It seems to be a very theoretical thing, far from our day-by-day reality.

Believe me. Modeling can be more practical than you might guess!

This talk will discuss the challenges and benefits of modeling, based on the experience of developing the PREEMPT_RT model. It will present a methodology for modeling the Linux behavior as Finite-State Machines (automata), using terms that are very known by kernel developers: tracing events! With the particular focus on how to use models for the formal verification of Linux kernel, at runtime, with low overhead, and in many cases, without even modifying Linux kernel!

Real-time micro-conference proposal for Linux Plumbers 2019

Last year we had a very fun and productive real-time micro-conference at the Linux Plumbers Conference, so the idea is to repeat it this year!

Are you interested in participating? Do you have any suggestion of topic? Let us know!

This is the current proposal of micro-conference, we can still edit it and add your thoughts.


Since 2004 a project has improved the Real-time and low-latency features for Linux. This project has become know as PREEMPT_RT, formally the real-time patch. Over the past decade, many parts of the PREEMPT RT became part of the official Linux code base. Examples of what came from PREEMPT_RT include: Real-time mutexes, high-resolution timers, lockdep, ftrace, RT scheduling, SCHED_DEADLINE, RCU_PREEMPT, generic interrupts, priority inheritance futexes, threaded interrupt handlers and more. The number of patches that needs integration has been reduced on the last years, and the pieces left are now mature enough to make its way into mainline Linux. This year could possibly be the year PREEMPT_RT is merged ™!

In the final lap of this race, the last patches are on the way to be merged, but there are still some pieces missing. When the merge occurs, the preempt-rt will start to follow a new pace: the Linus one. So, it is possible to raise the following discussions:

  1.  The status of the merge, and how can we resolve the last issues that block the merge;
  2. How can we improve the testing of the -rt, to follow the problems raised as Linus tree advances;
  3. What’s next?

Possible topics:

  • Status of the PREEMPT_RT Merge
  • Merge – what is missing and who can help?
  • How do we teach the rest of the kernel developers how not to break PREEMPT_RT?
  • Stable maintainers tools discussion & improvements.
  • Interrupt threads are RT and are not protected by the RT Throttling. How can we prevent interrupt thread starvation from a rogue RT task?
  • Improvements on full CPU isolation
  • Newer methods like proxy execution, hierarchical scheduler?
  • What tools can we add into tools/ that other kernel developers can use to test and learn about PREEMMPT_RT?
  • What tests can we add into tools/testing/selftests?
  • New tools for timing regression test, e.g. locking, overheads…
  • What kernel boot self-tests can be added?
  • Discuss various types of failures that can happen with PREEMPT_RT that normally would not happen in the vanilla kernel, e.g, with lockdep, preemption model.

I will suggest the continuation of the discussions of the topics I presented last year, based in the results of the work I did this year (spoiler: I am doing model verification in the kernel, and it is very efficient!).

Paul already told that he could talk about ongoing work to make RCU’s forward progress be more robust in overloaded cloud deployments. There will be some connection to real-time response involving rcu_poll and the infamous RCU kthread priority!

The continuation of the discussion of topics from last year’s micro-conference, including the development done during this (almost) year, are also welcome!

Early context tracking patch set: fixing perf & ftrace losing events

Some time ago, while using perf to check the automaton model, I noticed that perf was losing events. The same was reproducible with ftrace.

Steve pointed to a problem in the identification of the context execution used by the recursion control.

Currently, recursion control uses the preempt_counter to identify the current context. The NMI/HARD/SOFT IRQ counters are set in the preempt_counter in the irq_enter/exit functions.

In a trace, they are set like this:

 0)   ==========> |
 0)               |  do_IRQ() {		/* First C function */
 0)               |    irq_enter() {
 0)               |      		/* set the IRQ context. */
 0)   1.081 us    |    }
 0)               |    handle_irq() {
 0)               |     		/* IRQ handling code */
 0) + 10.290 us   |    }
 0)               |    irq_exit() {
 0)               |      		/* unset the IRQ context. */
 0)   6.657 us    |    }
 0) + 18.995 us   |  }
 0)   <========== |

As one can see, functions (and events) that take place before the set and after unset the preempt_counter are identified in the wrong context, causing the miss interpretation that recursion is taking place. When this happens, events are dropped.

To resolve this problem, the set/unset of the IRQ/NMI context needs to be done before the execution of the first C execution, and after its return. By doing so, and using this method to identify the context in the trace recursion protection, no more events are lost.

A possible solution is to use a per-cpu variable set and unset in the entry point of NMI/IRQs, before calling the C handler.

This possible solution is presented in this patch series as a proof of concept, for x86_64. Let’s see what kind of comments we will receive!

New tracepoints for External IRQ and NMIs

The irq_vectors class of tracepoints adds two events for each interrupt: One at the entry and one at the return of each interrupt handler. They are very useful in the analysis of latency, as they point to the occurrence of an interrupt, and how long did it take to run.

However, there are two cases of interrupt which these tracepoints were not present: NMIs and regular device interrupt. So I suggested two new tracepoints, for these cases.

The output of these new tracepoints looks like this:

 idle-0     [000] d.h.   102.890935: external_interrupt_entry: vector=35
 idle-0     [000] d.h.   102.890960: external_interrupt_exit: vector=35
 idle-0     [000] d.Z.   179.594315: nmi_entry: vector=2
 idle-0     [000] d.Z.   179.594396: nmi_exit: vector=2

The discussion of the patch set can be found here: