path: root/kernel/smpboot.c
diff options
authorChris Metcalf <>2015-06-24 16:55:45 -0700
committerLinus Torvalds <>2015-06-24 17:49:40 -0700
commitfe4ba3c34352b7e8068b7f18eb233444aed17011 (patch)
treed4b34e0d809e784c59eea68cb27c16dc795e371b /kernel/smpboot.c
parentb5242e98c1cb834feb1e84026f09a4796b49eb4d (diff)
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. [ 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 <>
Diffstat (limited to 'kernel/smpboot.c')
1 files changed, 1 insertions, 0 deletions
diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index 5e46c2a75d59..7c434c39f02a 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -338,6 +338,7 @@ EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
* The cpumask field in the smp_hotplug_thread must not be updated directly
* by the client, but only by calling this function.
+ * This function can only be called on a registered smp_hotplug_thread.
int smpboot_update_cpumask_percpu_thread(struct smp_hotplug_thread *plug_thread,
const struct cpumask *new)