The patch titled
Subject: smpboot: allow excluding cpus from the smpboot threads
has been added to the -mm tree. Its filename is
smpboot-allow-excluding-cpus-from-the-smpboot-threads.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/smpboot-allow-excluding-cpus-from-the-smpboot-threads.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/smpboot-allow-excluding-cpus-from-the-smpboot-threads.patch
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------------------------------------------------------
From: Chris Metcalf <cmetcalf@xxxxxxxxxx>
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/<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@xxxxxxxxxx>
Cc: Don Zickus <dzickus@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Ulrich Obergfell <uobergfe@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/smpboot.h | 5 +++
kernel/smpboot.c | 55 +++++++++++++++++++++++++++++++++++++-
2 files changed, 59 insertions(+), 1 deletion(-)
diff -puN include/linux/smpboot.h~smpboot-allow-excluding-cpus-from-the-smpboot-threads include/linux/smpboot.h
--- a/include/linux/smpboot.h~smpboot-allow-excluding-cpus-from-the-smpboot-threads
+++ a/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);
+ struct cpumask 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
diff -puN kernel/smpboot.c~smpboot-allow-excluding-cpus-from-the-smpboot-threads kernel/smpboot.c
--- a/kernel/smpboot.c~smpboot-allow-excluding-cpus-from-the-smpboot-threads
+++ a/kernel/smpboot.c
@@ -232,7 +232,8 @@ void smpboot_unpark_threads(unsigned int
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(stru
{
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 +291,7 @@ int smpboot_register_percpu_thread(struc
unsigned int cpu;
int ret = 0;
+ cpumask_copy(&plug_thread->cpumask, cpu_possible_mask);
get_online_cpus();
mutex_lock(&smpboot_threads_lock);
for_each_online_cpu(cpu) {
@@ -316,6 +327,48 @@ void smpboot_unregister_percpu_thread(st
}
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);
/*
_
Patches currently in -mm which might be from cmetcalf@xxxxxxxxxx are
origin.patch
smpboot-allow-excluding-cpus-from-the-smpboot-threads.patch
watchdog-add-watchdog_cpumask-sysctl-to-assist-nohz.patch
procfs-treat-parked-tasks-as-sleeping-for-task-state.patch
mm-hugetlb-reduce-arch-dependent-code-about-huge_pmd_unshare.patch
__bitmap_parselist-fix-bug-in-empty-string-handling.patch
linux-next.patch
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