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An AWS engineer reported a dramatic 50% performance drop for PostgreSQL on the upcoming Linux 7.0 kernel, caused by changes to kernel preemption modes. While a revert was proposed, kernel developers suggest PostgreSQL should adapt using Restartable Sequences (RSEQ). This could mean significant performance issues for databases on Linux 7.0 until PostgreSQL is updated.
This article details the journey of debugging mysterious system freezes caused by eBPF programs in the Linux kernel. We uncovered an issue where an NMI-driven eBPF sampling program would self-deadlock by attempting to acquire a spinlock already held by another eBPF program on the same CPU, leading to 250ms kernel timeouts. The analysis highlights the complexities of spinlocks, NMIs, and cache coherence in kernel development.
