Mourning Daniel Bristot de Oliveira

Daniel was a computer scientist with a focus on real-time systems and scheduling theory who is well recognized in the academic and the Linux kernel community. His truly outstanding ability to apply theoretical real-time concepts to real-world problems in the industry has been instrumental in driving the success of Linux and its adoption in real-time critical application spaces. While he pursued his ideas and visions with great perseverance, he was always open for discussion, criticism, and other people's ideas. His honesty, his modesty, and his wicked humor made it a pleasure to work with him. His wide interests outside of technology and his exceptional social skills made it easy to connect with him which resulted in many deep friendships reaching beyond the scope of work.

Daniel was creative and passionate about computer science. He earned a joint PhD from Universidade Federal de Santa Catarina in Brazil and Scuola Superiore Sant'Anna in Italy, with a research thesis focusing on Automata-based Formal Analysis and Verification of the Real-Time Linux Kernel. His work was an exemplary piece of research, combining theoretical research arguments with a real implementation of a kernel-level mechanism. It models the behavior of complex parts of the Linux kernel, such as the process scheduler, with a finite-state machine and uses minimum-overhead run-time verification to validate the coherence of the kernel's run-time behavior and the theoretical model.

Having Daniel at the ReTiS lab has been invaluable, as witnessed by various other collaborations that naturally developed while he was a PhD student, and later when he remained a Professional Affiliate at the lab. He helped mentor undergraduate and PhD students on various issues related to the performance and optimization of software running on Linux. He was also active in collaborating with various other research groups working on system-level topics, as witnessed by his co-authored papers.

Daniel started contributing to the development of the SCHED_DEADLINE scheduling policy by fixing all sorts of issues, demonstrating from the start a deep understanding of both the technical and theoretical details of the implementation. Not long after, he stepped up to the role of co-maintainer of the project, taking on a big portion of the recent work on new features for the scheduler.

RTLA (Real-Time Linux Analysis toolset) and RV (Runtime Verification) are just two outstanding examples of Daniel's work in Linux. RTLA is a meta-tool that binds the timerlat, osnoise, and hwnoise tracers into a single, user-friendly, command-line application.

• The timerlat tracer helps find the sources of wakeup latencies affecting real-time threads. Similar to cyclictest, it uses a periodic timer to catch and measure latency spikes, but timerlat provides greater level of detail and a more precise picture of the various contributions to latency at different levels (including interrupts, kernel, and user space).
• The osnoise tracer runs a busy-loop workload in the kernel, with preemption, soft and hard interrupts enabled. By taking note of the entry and exit point of any source of interference, it produces a fine-grained analysis of the potential sources of system noise that a polling application (e.g., HPC, DPDK) can suffer from.
• Last but not least, the hwnoise tool (based on the osnoise tracer) is essentially meant as a replacement for hwlatdetect, extending coverage to multiple scenarios (including round-robin, per-CPU, and a subset of CPUs) and, again, increasing the level of detail in the report.

RV is a lightweight yet rigorous method that complements classical exhaustive verification techniques, such as model checking and theorem proving, with a more practical approach for complex systems. Instead of relying on a fine-grained model of a system, such as a re-implementation at instruction level, RV works by analyzing the trace of the system's actual execution and comparing it against a formal specification of the system's behavior. Daniel pioneered the method of using an RV Monitor as an active safety mechanism in the kernel with the ELISA (Enabling Linux in Safety Critical Applications) community. He also generously shared how the RTLA tools could be used to isolate a workload from interference from the rest of the system in one of the first seminars the project held.

Daniel has been deeply involved in organizing several conferences over the years. Many discussions with key outcomes could not have happened without his tireless work inviting people, putting together schedules, and making sure people were constantly focusing on arguments that matter rather than digressing into pointless arguing. He used his natural talent for jokes and witty comments to make everyone relax, feel at ease, and feel welcome to contribute to the discussion. To name a few, knowing it's going to be only a partial list, he helped organized the Linux Plumbers Real-time and Scheduler micro-conferences, Power Management and Scheduling in the Linux Kernel (OSPM) Summit and the Real-Time Linux Summit; he has also been in the technical program committee of top conferences in real-time systems research, such as RTSS, RTAS and ECRTS.

The Brazilian lyricist Paolo Coelho wrote: "Never. We never lose our loved ones. They accompany us; they don't disappear from our lives. We are merely in different rooms." The academic and Linux kernel communities will always be accompanied by Daniel and by the traces he left in his work and in our hearts. Our hearts and thoughts are with Daniel's fiance and family.

If you want to express your condolences please send an email to [email protected]. It will be passed on to the ones who he loved most.