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authorChris Metcalf <cmetcalf@ezchip.com>2015-06-24 16:55:42 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-06-24 17:49:40 -0700
commitb5242e98c1cb834feb1e84026f09a4796b49eb4d (patch)
tree46f415a3fb41a6238f8e6d69675d2e22960c3447 /kernel/smpboot.c
parent8c07a308ec5284fe41aefe48ac2ef4cfcd71ddbf (diff)
downloadlinux-sh-b5242e98c1cb834feb1e84026f09a4796b49eb4d.tar.gz
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>
Diffstat (limited to 'kernel/smpboot.c')
-rw-r--r--kernel/smpboot.c59
1 files changed, 58 insertions, 1 deletions
diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index c697f73d82d6..5e46c2a75d59 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -232,7 +232,8 @@ void smpboot_unpark_threads(unsigned int cpu)
mutex_lock(&smpboot_threads_lock);
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);
}
@@ -258,6 +259,15 @@ static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
{
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 */
for_each_possible_cpu(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)
unsigned int cpu;
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();
mutex_lock(&smpboot_threads_lock);
for_each_online_cpu(cpu) {
@@ -313,9 +327,52 @@ void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
smpboot_destroy_threads(plug_thread);
mutex_unlock(&smpboot_threads_lock);
put_online_cpus();
+ free_cpumask_var(plug_thread->cpumask);
}
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);
/*