This book constitutes the refereed proceedings of the 20th European Workshop on Computer Performance Engineering, EPEW 2024, held in Venice, Italy, on June 14, 2024. The 10 papers presented in this volume together with one invited talk were carefully reviewed and selected from 14 submissions. The concept of performance in EPEW 2024 is considered in its broadest sense including the notions of Quality of Service, scalability as well as reliability, availability and systems management, among the others.