Linux 7.0 Preemption Change Causes 50% PostgreSQL Throughput Drop on Graviton4
By
Teiva Harsanyi
Crisp on the outside, thoughtful on the inside. A keeper.
Summary
A Linux kernel preemption change introduced in version 7.0 caused PostgreSQL throughput to drop by roughly 50% on AWS Graviton4 96-vCPU machines. The regression stems from how the new preemption model interacts with PostgreSQL's spinlock-based memory management, exposing a critical bottleneck. AWS engineer Salvatore Dipietro identified the issue via pgbench benchmarking and posted a patch to the Linux kernel mailing list on April 3, 2026. The article explains the technical root cause from first principles, tracing the interaction between kernel preemption behavior, memory page management, and PostgreSQL's internal locking mechanisms.
Key quotes
· 3 pulledon a 96-vCPU Graviton4 machine running Linux 7.0, PostgreSQL throughput had dropped to roughly half of what it produced on Linux 6.x
Salvatore Dipietro ran pgbench (PostgreSQL's standard benchmarking tool) on a Graviton4 processor with 96 vCPUs
Salvatore Dipietro, an engineer at AWS, posted a patch to the Linux kernel mailing list
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