Decoding Those Inscrutable RCU CPU Stall Warnings

Presented by Paul E. McKenney
Monday 4:35 p.m.–5 p.m. in Great Hall CB01.05.009
Target audience: Developer

Abstract

You are minding your own business when suddenly one of your system splats out something like "INFO: rcu_bh_state detected stalls on CPUs/tasks: { 3 5 } (detected by 2, 2502 jiffies)". Whatever does this RCU CPU stall warning mean and what can you do about it? That is, other than simply beating your head against Documentation/RCU/stallwarn.txt? This talk will look at a few representative RCU CPU stall warning messages and show how they can be decoded into real information that can help you find otherwise silent hangs the easy way. Or at least an easier way!

Presented by

Paul E. McKenney

Paul E. McKenney is a Distinguished Engineer with the IBM Linux Technology Center, where he maintains the RCU implementation within the Linux kernel. He has been coding for four decades, and more than half of that on parallel hardware. His prior lives include working on the DYNIX/ptx kernel at Sequent, work on packet radio, Internet protocols, and system administration at SRI International, and work on soft-realtime systems as a self-employed contract programmer. His hobbies include what passes for running at his age (AKA hiking) along with the usual house-wife-and-grown-kids habit.