Commit b5242e98 authored by Chris Metcalf's avatar Chris Metcalf Committed by Linus Torvalds

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: default avatarChris 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8c07a308
...@@ -27,6 +27,8 @@ struct smpboot_thread_data; ...@@ -27,6 +27,8 @@ struct smpboot_thread_data;
* @pre_unpark: Optional unpark function, called before the thread is * @pre_unpark: Optional unpark function, called before the thread is
* unparked (cpu online). This is not guaranteed to be * unparked (cpu online). This is not guaranteed to be
* called on the target cpu of the thread. Careful! * 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. * @selfparking: Thread is not parked by the park function.
* @thread_comm: The base name of the thread * @thread_comm: The base name of the thread
*/ */
...@@ -41,11 +43,14 @@ struct smp_hotplug_thread { ...@@ -41,11 +43,14 @@ struct smp_hotplug_thread {
void (*park)(unsigned int cpu); void (*park)(unsigned int cpu);
void (*unpark)(unsigned int cpu); void (*unpark)(unsigned int cpu);
void (*pre_unpark)(unsigned int cpu); void (*pre_unpark)(unsigned int cpu);
cpumask_var_t cpumask;
bool selfparking; bool selfparking;
const char *thread_comm; const char *thread_comm;
}; };
int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread); int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread);
void smpboot_unregister_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 #endif
...@@ -232,7 +232,8 @@ void smpboot_unpark_threads(unsigned int cpu) ...@@ -232,7 +232,8 @@ void smpboot_unpark_threads(unsigned int cpu)
mutex_lock(&smpboot_threads_lock); mutex_lock(&smpboot_threads_lock);
list_for_each_entry(cur, &hotplug_threads, list) list_for_each_entry(cur, &hotplug_threads, list)
smpboot_unpark_thread(cur, cpu); if (cpumask_test_cpu(cpu, cur->cpumask))
smpboot_unpark_thread(cur, cpu);
mutex_unlock(&smpboot_threads_lock); mutex_unlock(&smpboot_threads_lock);
} }
...@@ -258,6 +259,15 @@ static void smpboot_destroy_threads(struct smp_hotplug_thread *ht) ...@@ -258,6 +259,15 @@ static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
{ {
unsigned int cpu; unsigned int cpu;
/* Unpark any threads that were voluntarily parked. */
for_each_cpu_not(cpu, ht->cpumask) {
if (cpu_online(cpu)) {
struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
if (tsk)
kthread_unpark(tsk);
}
}
/* We need to destroy also the parked threads of offline cpus */ /* We need to destroy also the parked threads of offline cpus */
for_each_possible_cpu(cpu) { for_each_possible_cpu(cpu) {
struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
...@@ -281,6 +291,10 @@ int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread) ...@@ -281,6 +291,10 @@ int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
unsigned int cpu; unsigned int cpu;
int ret = 0; int ret = 0;
if (!alloc_cpumask_var(&plug_thread->cpumask, GFP_KERNEL))
return -ENOMEM;
cpumask_copy(plug_thread->cpumask, cpu_possible_mask);
get_online_cpus(); get_online_cpus();
mutex_lock(&smpboot_threads_lock); mutex_lock(&smpboot_threads_lock);
for_each_online_cpu(cpu) { for_each_online_cpu(cpu) {
...@@ -313,9 +327,52 @@ void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread) ...@@ -313,9 +327,52 @@ void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
smpboot_destroy_threads(plug_thread); smpboot_destroy_threads(plug_thread);
mutex_unlock(&smpboot_threads_lock); mutex_unlock(&smpboot_threads_lock);
put_online_cpus(); put_online_cpus();
free_cpumask_var(plug_thread->cpumask);
} }
EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread); EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
/**
* smpboot_update_cpumask_percpu_thread - Adjust which per_cpu hotplug threads stay parked
* @plug_thread: Hotplug thread descriptor
* @new: Revised mask to use
*
* The cpumask field in the smp_hotplug_thread must not be updated directly
* by the client, but only by calling this function.
*/
int smpboot_update_cpumask_percpu_thread(struct smp_hotplug_thread *plug_thread,
const struct cpumask *new)
{
struct cpumask *old = plug_thread->cpumask;
cpumask_var_t tmp;
unsigned int cpu;
if (!alloc_cpumask_var(&tmp, GFP_KERNEL))
return -ENOMEM;
get_online_cpus();
mutex_lock(&smpboot_threads_lock);
/* Park threads that were exclusively enabled on the old mask. */
cpumask_andnot(tmp, old, new);
for_each_cpu_and(cpu, tmp, cpu_online_mask)
smpboot_park_thread(plug_thread, cpu);
/* Unpark threads that are exclusively enabled on the new mask. */
cpumask_andnot(tmp, new, old);
for_each_cpu_and(cpu, tmp, cpu_online_mask)
smpboot_unpark_thread(plug_thread, cpu);
cpumask_copy(old, new);
mutex_unlock(&smpboot_threads_lock);
put_online_cpus();
free_cpumask_var(tmp);
return 0;
}
EXPORT_SYMBOL_GPL(smpboot_update_cpumask_percpu_thread);
static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD); static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD);
/* /*
......
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