From b5242e98c1cb834feb1e84026f09a4796b49eb4d Mon Sep 17 00:00:00 2001 From: Chris Metcalf Date: Wed, 24 Jun 2015 16:55:42 -0700 Subject: smpboot: allow excluding cpus from the smpboot threads This patch series allows the watchdog to run by default only on the housekeeping cores when nohz_full is in effect; this seems to be a good compromise short of turning it off completely (since the nohz_full cores can't tolerate a watchdog). To provide customizability, we add /proc/sys/kernel/watchdog_cpumask so that the set of cores running the watchdog can be tuned to different values after bootup. To implement this customizability, we add a new smpboot_update_cpumask_percpu_thread() API to the smpboot_thread subsystem that lets us park or unpark "unwanted" threads. And now that threads can be parked for long periods of time, we tweak the /proc//stat and /proc//status code so parked threads aren't reported as running, which is otherwise confusing. This patch (of 3): This change allows some cores to be excluded from running the smp_hotplug_thread tasks. The following commit to update kernel/watchdog.c to use this functionality is the motivating example, and more information on the motivation is provided there. A new smp_hotplug_thread field is introduced, "cpumask", which is cpumask field managed by the smpboot subsystem that indicates whether or not the given smp_hotplug_thread should run on that core; the cpumask is checked when deciding whether to unpark the thread. To limit the cpumask to less than cpu_possible, you must call smpboot_update_cpumask_percpu_thread() after registering. Signed-off-by: Chris Metcalf Cc: Don Zickus Cc: Ingo Molnar Cc: Ulrich Obergfell Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Frederic Weisbecker Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/smpboot.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include/linux/smpboot.h') diff --git a/include/linux/smpboot.h b/include/linux/smpboot.h index d600afb21926..da3c593f9845 100644 --- a/include/linux/smpboot.h +++ b/include/linux/smpboot.h @@ -27,6 +27,8 @@ struct smpboot_thread_data; * @pre_unpark: Optional unpark function, called before the thread is * unparked (cpu online). This is not guaranteed to be * called on the target cpu of the thread. Careful! + * @cpumask: Internal state. To update which threads are unparked, + * call smpboot_update_cpumask_percpu_thread(). * @selfparking: Thread is not parked by the park function. * @thread_comm: The base name of the thread */ @@ -41,11 +43,14 @@ struct smp_hotplug_thread { void (*park)(unsigned int cpu); void (*unpark)(unsigned int cpu); void (*pre_unpark)(unsigned int cpu); + cpumask_var_t cpumask; bool selfparking; const char *thread_comm; }; int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread); void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread); +int smpboot_update_cpumask_percpu_thread(struct smp_hotplug_thread *plug_thread, + const struct cpumask *); #endif -- cgit v1.2.3