Senior Performance Modeling Engineer

Job Description

Company Overview

Flux Computing designs and manufactures optical processors to train and run inference on large AI models. Join us in London to be part of a highly motivated and skilled team that thrives on delivering impact and innovation at speed.

The Role

We’re searching for a Performance Modeling Engineer to create and own the analytical and simulation models that steer OTPU architecture and software evolution. You will build functional simulators as well as high-fidelity, cycle-accurate models of our optical compute system. This role is critical to explore “what-if” design spaces, and deliver insights that directly influence our software, hardware, and optical roadmaps. This role sits at the crossroads of hardware architecture, software tooling and machine-learning workload analysis, perfect for an engineer who loves data-driven decision-making and fast iteration.

Responsibilities

• Project Ownership: Own and deliver projects on your team's roadmap that unlock key high-impact technical and business milestones that drive the success of Flux.
• Collaboration: Work shoulder-to-shoulder with hardware, compiler and ML framework teams to ensure models reflect reality and reality meets performance goals.
• Functional Simulator: Design, build, and maintain a functional simulator of the OPTU subsystem and full pipeline. 
• Performance Simulator: Design and maintain architectural & cycle-accurate models of the OPTU subsystems and pipeline. Identify throughput, latency and utilisation hot-spots; propose architectural, or scheduling fixes.
• Workload Analysis & Bottleneck Hunting: Instrument benchmarks (LLMs, diffusion, graph workloads) to collect detailed traces.
• Design-Space Exploration: Run massive parameter sweeps with your functional and to understand tradeoffs and guide the software, hardware, and optical teams. Package results into clear, quantitative analyses and design recommendations.
• Tooling & Automation: Develop Python/C++ tooling for trace parsing, statistical analysis and visualisation. Integrate models into CI so that every RTL commit gets a performance smoke test.

Skills & Experience

• 5+ years building performance or power models for CPUs, GPUs, ASICs, or accelerators
• Strong coding ability in C++ and Python; experience with discrete-event or cycle-accurate simulators (e.g., gem5, SystemC, custom in-house).
• Solid grasp of computer-architecture fundamentals: memory systems, interconnects, queuing theory, Amdahl/Gustafson analysis.
• Familiarity with machine-learning workloads and common frameworks (PyTorch, TensorFlow, JAX).
• Comfort reading RTL or schematics and discussing micro-architectural trade-offs with hardware designers.
• Excellent data-visualisation and communication skills: able to turn millions of simulation samples into one decisive slide.
• Bachelor’s+ in EE, CS, Physics, Applied Maths or related; advanced degree but not required.
• Personal or open-source projects in simulators, ML kernels, or performance analysis are a significant plus.

Compensation & Benefits

• Competitive salary and stock options in a rapidly growing AI company.
• Based in our new 5,000 sq. ft. office in the AI hub of Kings Cross, London.
• To foster collaboration in our high-growth environment, we require all employees to work from our London HQ and live within a 45-minute commute. We offer an extra £24,000/year incentive for those living within 20 minutes.
• Comprehensive healthcare insurance.
• 25 days PTO policy plus bank holidays.
• Private access to our in-house 3D printer.

If you are passionate about pushing the boundaries of what's possible in AI and thrive in a high-energy, fast-paced environment, we want to hear from you. Apply now to join Flux and be a key player in shaping the future of computing.