EE ZOOM Seminar: Optimizing Multi-Core Read Latency in ccNUMA Systems
https://tau-ac-il.zoom.us/j/87072113850
Electrical Engineering Systems ZOOM Seminar
Speaker: Alla Lenchner
M.Sc. student under the supervision of Prof. Adam Morrison
Wednesday, 6th August 2025, at 15:00
Optimizing Multi-Core Read Latency in ccNUMA Systems
Abstract
Non-Uniform Memory Access (NUMA) architectures present challenges for efficient system utilization, particularly in data-intensive, read-heavy workloads common in big data analytics and machine learning.
While read operations are theoretically scalable, this thesis reveals a significant and unexpected degradation in memory read latency for multi-core read-heavy workloads on ccNUMA systems, extending beyond the known "NUMA effect."
This issue stems from a problematic interaction within Intel's directory-based cache coherence protocol: silent evictions of exclusively cached but unmodified data leave stale entries in the coherence directory. Subsequent requests for exclusive ownership of these cache lines incur redundant inter-node round trips, unnecessarily increasing access latency.
This thesis investigates this phenomenon, analyzing the latency impact of inter-node traffic and cache coherence overheads.
We detail the interaction between the Exclusive state and silent evictions, providing a theoretical analysis of its latency implications.
We also examine an existing BIOS-configurable optimization by Intel, demonstrating its benefit for read-heavy workloads but highlighting its detrimental effect on read-write workloads.
To address this, we propose a novel micro-architectural solution: an adaptive directory state mechanism.
This mechanism aims to reduce redundant coherence traffic for cache lines affected by silent evictions without negatively impacting read-write performance. Evaluation through gem5 simulations demonstrates that our proposed solution achieves a 16\% reduction in memory read latency for the affected workloads.
Alla Lenchner is an M.Sc. student specializing in CPU performance and architecture.
השתתפות בסמינר תיתן קרדיט שמיעה = עפ"י רישום בצ'ט של שם מלא + מספר ת.ז.
