From 67182ae1c42206e516f7efb292b745e826497b24 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sun, 10 Aug 2008 18:35:38 -0700 Subject: rcu, debug: detect stalled grace periods this is a diagnostic patch for Classic RCU. The approach is to record a timestamp at the beginning of the grace period (in rcu_start_batch()), then have rcu_check_callbacks() complain if: 1. it is running on a CPU that has holding up grace periods for a long time (say one second). This will identify the culprit assuming that the culprit has not disabled hardware irqs, instruction execution, or some such. 2. it is running on a CPU that is not holding up grace periods, but grace periods have been held up for an even longer time (say two seconds). It is enabled via the default-off CONFIG_DEBUG_RCU_STALL kernel parameter. Rather than exponential backoff, it backs off to once per 30 seconds. My feeling upon thinking on it was that if you have stalled RCU grace periods for that long, a few extra printk() messages are probably the least of your worries... Signed-off-by: Paul E. McKenney Cc: Peter Zijlstra Cc: Yinghai Lu Cc: David Witbrodt Signed-off-by: Ingo Molnar --- lib/Kconfig.debug | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'lib/Kconfig.debug') diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index e1d4764435ed..2fb6d90bf1e6 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -597,6 +597,19 @@ config RCU_TORTURE_TEST_RUNNABLE Say N here if you want the RCU torture tests to start only after being manually enabled via /proc. +config RCU_CPU_STALL + bool "Check for stalled CPUs delaying RCU grace periods" + depends on CLASSIC_RCU + default n + help + This option causes RCU to printk information on which + CPUs are delaying the current grace period, but only when + the grace period extends for excessive time periods. + + Say Y if you want RCU to perform such checks. + + Say N if you are unsure. + config KPROBES_SANITY_TEST bool "Kprobes sanity tests" depends on DEBUG_KERNEL -- cgit v1.2.1