From fe4ba3c34352b7e8068b7f18eb233444aed17011 Mon Sep 17 00:00:00 2001 From: Chris Metcalf Date: Wed, 24 Jun 2015 16:55:45 -0700 Subject: watchdog: add watchdog_cpumask sysctl to assist nohz Change the default behavior of watchdog so it only runs on the housekeeping cores when nohz_full is enabled at build and boot time. Allow modifying the set of cores the watchdog is currently running on with a new kernel.watchdog_cpumask sysctl. In the current system, the watchdog subsystem runs a periodic timer that schedules the watchdog kthread to run. However, nohz_full cores are designed to allow userspace application code running on those cores to have 100% access to the CPU. So the watchdog system prevents the nohz_full application code from being able to run the way it wants to, thus the motivation to suppress the watchdog on nohz_full cores, which this patchset provides by default. However, if we disable the watchdog globally, then the housekeeping cores can't benefit from the watchdog functionality. So we allow disabling it only on some cores. See Documentation/lockup-watchdogs.txt for more information. [jhubbard@nvidia.com: fix a watchdog crash in some configurations] Signed-off-by: Chris Metcalf Acked-by: Don Zickus Cc: Ingo Molnar Cc: Ulrich Obergfell Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Frederic Weisbecker Signed-off-by: John Hubbard Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/nmi.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'include/linux/nmi.h') diff --git a/include/linux/nmi.h b/include/linux/nmi.h index 3d46fb4708e0..f94da0e65dea 100644 --- a/include/linux/nmi.h +++ b/include/linux/nmi.h @@ -67,6 +67,7 @@ extern int nmi_watchdog_enabled; extern int soft_watchdog_enabled; extern int watchdog_user_enabled; extern int watchdog_thresh; +extern unsigned long *watchdog_cpumask_bits; extern int sysctl_softlockup_all_cpu_backtrace; struct ctl_table; extern int proc_watchdog(struct ctl_table *, int , @@ -77,6 +78,8 @@ extern int proc_soft_watchdog(struct ctl_table *, int , void __user *, size_t *, loff_t *); extern int proc_watchdog_thresh(struct ctl_table *, int , void __user *, size_t *, loff_t *); +extern int proc_watchdog_cpumask(struct ctl_table *, int, + void __user *, size_t *, loff_t *); #endif #ifdef CONFIG_HAVE_ACPI_APEI_NMI -- cgit v1.2.3-59-g8ed1b