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/<pid>/stat and /proc/<pid>/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 <cmetcalf@ezchip.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/smpboot.h b/include/linux/smpboot.h
index d600afb..da3c593 100644
--- a/include/linux/smpboot.h
+++ b/include/linux/smpboot.h
@@ -27,6 +27,8 @@
* @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 @@
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