Senior Performance Modelling Engineer

Flux • San Francisco, CA

29d • $230,000 - $282,000 • Onsite

About The Position

We’re searching for a Senior Performance Modelling Engineer (San Francisco) 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.

Requirements

• 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 preferred but not required.

Nice To Haves

• Personal or open-source projects in simulators, ML kernels, or performance analysis are a significant plus.

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.

Benefits

• Generous stock options in a rapidly growing AI company
• Based in our office in central San Francisco
• To foster collaboration in our high-growth environment, we require all employees to work from our SF office and live within a 45-minute commute. We offer an extra ($24,000/year) incentive for those living within 20 minutes.

What This Job Offers

• Job Type: Full-time
• Career Level: Senior