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Hiring Guide 7 min read

What to Look For in a Low-Latency C++ or Rust Developer

Hiring a low-latency developer? Look for lock-free data structures, cache optimization, kernel bypass, and microseconds-obsessed mindset. Here's your interview checklist.

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The Microsecond Difference Must-Have Skills for Low-Latency Development Red Flags That Should Stop Your Interview 5 Interview Questions That Separate the Best Senior vs Junior in Low-Latency Don't Settle for 'Fast Enough'

Your trading system is slow. Orders arrive late. Market data lags. You need a low-latency developer - but how do you separate the real experts from the pretenders? This guide gives you a practical checklist for interviewing C++ and Rust developers for low-latency roles.

Must-Have Skills for Low-Latency Development

A real low-latency developer understands:

  • ✦ Cache locality and memory layout (data-oriented design)
  • ✦ Lock-free and wait-free data structures
  • ✦ CPU cache hierarchy (L1, L2, L3 - size and latency)
  • ✦ Branch prediction and how to write branch-predictable code
  • ✦ False sharing and cache line padding
  • ✦ NUMA awareness for multi-socket systems

Tools Strong Candidates Commonly Use

  • ✦ perf
  • ✦ FlameGraph
  • ✦ Valgrind
  • ✦ Intel VTune
  • ✦ Benchmark frameworks
  • ✦ Network packet analyzers

Red Flags That Should Stop Your Interview

Walk away if the candidate:

  • ✦ Uses std::mutex without understanding lock-free alternatives
  • ✦ Can't explain the difference between user-space and kernel-space
  • ✦ Has never heard of DPDK or io_uring
  • ✦ Thinks 'low-latency' means sub-100ms
  • ✦ Uses dynamic memory allocation in the hot path

5 Interview Questions That Separate the Best

False sharing happens when two threads write to different variables that share the same cache line. Detection: perf stat, cache line padding. Fix: align variables to cache line boundaries (usually 64 bytes).
Memory reclamation (ABA problem), ring buffer design, multi-producer multi-consumer vs single-producer single-consumer, and memory ordering (acquire/release semantics).
TSC for nanosecond timing, flame graphs for profiling, measure P99 and maximum (not just average). Reduce: avoid system calls, batch operations, use kernel bypass.

Senior vs Junior in Low-Latency

Lock-free

Junior: Knows it exists, maybe used atomics
Senior: Has implemented multiple lock-free structures, knows ABA problem solutions

Profiling

Junior: Uses basic timers
Senior: Uses perf, flame graphs, TSC, understands measurement bias

Kernel Bypass

Junior: Knows the term
Senior: Has implemented DPDK or io_uring solutions

C++/Rust

Junior: Writes idiomatic code
Senior: Optimizes memory layout, uses placement new, custom allocators

Projects That Demonstrate Real Low-Latency Experience

  • ✦ Exchange gateways
  • ✦ Market data handlers
  • ✦ Matching engines
  • ✦ Real-time analytics systems
  • ✦ Custom networking stacks

Don't Settle for 'Fast Enough'

In trading, 'fast enough' doesn't exist. Every microsecond of latency is lost profit. Hire developers who obsess over performance. Offline Pixel has pre-vetted low-latency C++ and Rust developers. Raise a request and we'll match you within 8 hours. Talk to candidates. Fund the project. Approve payment when the work is complete.

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