#performance

13 performance interview questions, asked at Nvidia, Apple, Amazon and 7 more companies. Last asked Oct 2026.

Review a CSV-building function for correctness and performance bugsCodingYou are shown a short function (in Java or Python) that turns a table, a list of rows of string cells, into CSV text by appending to a string in a loop. Say what is wrong with its…
Last asked Oct 2026
Diagnose a slow Linux server: CPU, disk, network and logsCodingA troubleshooting round in several scenarios. For each, say which tools you reach for, what the numbers tell you and how you get from the host down to the cause. 1. CPU looks…
Last asked Sep 2026
Roofline analysis of a BF16 MLP layerML designApply roofline analysis to an MLP layer running in BF16: count its floating-point operations and the bytes it moves, compute its arithmetic intensity, and decide whether it is…
Last asked Aug 2026
GPU and inference performance fundamentalsML designAnswer questions on GPU performance: Amdahl's law, HBM versus on-chip SRAM, matrix-multiply cost and tiling, CPU versus GPU execution, tensor and pipeline parallelism, and where…
Last asked Aug 2026
Diagnose a slow cold load and a huge table in a web appCodingA web app is slow on its first load, and one page renders a table with a very large number of rows that makes the page sluggish. Explain how you would find the causes (profiling…
Last asked Jul 2026
Sort a hundred million digitsCodingYou need to sort one hundred million single digits. How do you do it fast? Explain why a general comparison sort is the wrong tool here, what to use instead, and how memory and…
Last asked Jul 2026
Transpose a matrix and reason about memory layoutCodingTranspose a square or rectangular matrix, in place where possible. Then discuss row-major versus column-major storage, cache behaviour, and how to make the transpose fast for very…
Last asked Apr 2026
Write and speed up an image filter for on-device useML designWrite an image filter (a convolution over pixels, such as a blur) and make it fast enough to run on a device. Discuss the cost per pixel, separable kernels, edge handling, memory…
Last asked Mar 2026
Speed up a byte tokenizer and estimate token countsCodingYou are given a slow but correct reference tokenizer over bytes. Explain precisely what it does, then write a faster version that returns identical output. Finally, estimate the…
Last asked Jan 2026
Optimize a small-string class in C++CodingBuild a high-performance C++ string class for a workload with very many strings, supporting operations such as compare, concatenate and substring. Short strings live in a…
Last asked Dec 2025
Debug performance problems in a distributed systemSystem designA distributed service has become slow. Walk through how you find out why: metrics, tracing and logs, finding the slow component, common causes (hot partitions, lock contention…
Last asked Dec 2025
C++ performance round with provided threading codeCodingA 60-minute coding round for performance-minded roles, held in C++. The focus is on core C++ performance, with a smaller part on concurrency; the threading components are…
Last asked Sep 2025
Find bugs and slow renders in a React appCodingYou get a small React codebase with several bugs and performance problems. Find and fix them: unnecessary re-renders, event listeners that are never cleaned up, and similar…
Last asked Aug 2025