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Qualcomm·Software Engineer·Technical Phone Screen·Senior

Senior
Jun 2026

Summary

Interviewed for a GPU Engineer role at Qualcomm. The technical question was deep and pretty open-ended, covering GPU optimization at a level where knowing the buzzwords isn't enough. Came out feeling like I left some things on the table.

Questions Asked (1)

Q1

If a GPU kernel applies the same uniform operation across all threads, how would you improve its performance and power efficiency?

System DesignTechnical Trade-offs
Author's notes

This one sprawled in a lot of directions.

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AI HintsAI Generated

Suggested Approach

Start by identifying that uniform operations across all threads indicate SIMT inefficiency where all threads execute identical work, so you should propose scalarizing or offloading the operation to a dedicated unit. Then discuss trade-offs between using scalar/control processors, reducing thread divergence, and leveraging hardware features like uniform datapath or special function units to save power and cycles.

Pro tip: Mention that Qualcomm's Adreno GPUs have a dedicated scalar/control processor and uniform datapath that can execute uniform operations once instead of per-thread, which directly improves both performance and power efficiency—showing you understand their architecture.

1. Identify the inefficiency

Explain that when all threads perform the same operation, the SIMT execution model wastes resources by replicating the operation across all lanes. This leads to redundant computation and higher power consumption.

2. Propose scalarization or uniform datapath

Suggest moving the uniform operation to a scalar unit or uniform datapath that executes once for the entire warp/wavefront, reducing instruction issue and execution overhead.

3. Consider offloading to CPU or dedicated hardware

If the operation is truly uniform and independent, offload it to the CPU or a fixed-function unit (e.g., a special function unit) to free GPU resources and save power.

4. Evaluate trade-offs and alternatives

Discuss trade-offs: scalarization may add latency or synchronization overhead; offloading may incur data transfer costs. Compare with other optimizations like loop unrolling or vectorization.

5. Quantify benefits and conclude

Summarize expected gains: reduced instruction count, lower power due to fewer active lanes, and better utilization. Mention profiling to validate improvements.

Key Points to Mention

  • SIMT execution model and thread divergence
  • Uniform datapath or scalar unit in GPU architectures (e.g., Adreno's scalar processor)
  • Power efficiency from reducing active lanes and instruction issue
  • Offloading uniform work to CPU or fixed-function hardware
  • Trade-offs: latency, synchronization, data transfer overhead
  • Profiling tools to measure performance and power impact

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.