The patch titled
hotplug cpu: migrate a task within its cpuset
has been added to the -mm tree. Its filename is
hotplug-cpu-migrate-a-task-within-its-cpuset.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: hotplug cpu: migrate a task within its cpuset
From: Cliff Wickman <cpw@xxxxxxx>
When a cpu is disabled, move_task_off_dead_cpu() is called for tasks that have
been running on that cpu.
Currently, such a task is migrated:
1) to any cpu on the same node as the disabled cpu, which is both online
and among that task's cpus_allowed
2) to any cpu which is both online and among that task's cpus_allowed
It is typical of a multithreaded application running on a large NUMA system to
have its tasks confined to a cpuset so as to cluster them near the memory that
they share. Furthermore, it is typical to explicitly place such a task on a
specific cpu in that cpuset. And in that case the task's cpus_allowed
includes only a single cpu.
This patch would insert a preference to migrate such a task to some cpu within
its cpuset (and set its cpus_allowed to its entire cpuset).
With this patch, migrate the task to:
1) to any cpu on the same node as the disabled cpu, which is both online
and among that task's cpus_allowed
2) to any online cpu within the task's cpuset
3) to any cpu which is both online and among that task's cpus_allowed
In order to do this, move_task_off_dead_cpu() must make a call to
cpuset_cpus_allowed_locked(), a new subset of cpuset_cpus_allowed(), that will
not block. (name change - per Oleg's suggestion)
Calls are made to cpuset_lock() and cpuset_unlock() in migration_call() to set
the cpuset mutex during the whole migrate_live_tasks() and
migrate_dead_tasks() procedure.
This patch depends on 2 patches from Oleg Nesterov:
[PATCH 1/2] do CPU_DEAD migrating under read_lock(tasklist) instead of write_lock_irq(tasklist)
[PATCH 2/2] migration_call(CPU_DEAD): use spin_lock_irq() instead of task_rq_lock()
Signed-off-by: Cliff Wickman <cpw@xxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Christoph Lameter <clameter@xxxxxxx>
Cc: Paul Jackson <pj@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/cpuset.h | 5 +++++
kernel/cpuset.c | 15 ++++++++++++++-
kernel/sched.c | 12 +++++++++++-
3 files changed, 30 insertions(+), 2 deletions(-)
diff -puN include/linux/cpuset.h~hotplug-cpu-migrate-a-task-within-its-cpuset include/linux/cpuset.h
--- a/include/linux/cpuset.h~hotplug-cpu-migrate-a-task-within-its-cpuset
+++ a/include/linux/cpuset.h
@@ -21,6 +21,7 @@ extern int cpuset_init_early(void);
extern int cpuset_init(void);
extern void cpuset_init_smp(void);
extern cpumask_t cpuset_cpus_allowed(struct task_struct *p);
+extern cpumask_t cpuset_cpus_allowed_locked(struct task_struct *p);
extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
#define cpuset_current_mems_allowed (current->mems_allowed)
void cpuset_init_current_mems_allowed(void);
@@ -86,6 +87,10 @@ static inline cpumask_t cpuset_cpus_allo
{
return cpu_possible_map;
}
+static inline cpumask_t cpuset_cpus_allowed_locked(struct task_struct *p)
+{
+ return cpu_possible_map;
+}
static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
{
diff -puN kernel/cpuset.c~hotplug-cpu-migrate-a-task-within-its-cpuset kernel/cpuset.c
--- a/kernel/cpuset.c~hotplug-cpu-migrate-a-task-within-its-cpuset
+++ a/kernel/cpuset.c
@@ -1466,10 +1466,23 @@ cpumask_t cpuset_cpus_allowed(struct tas
cpumask_t mask;
mutex_lock(&callback_mutex);
+ mask = cpuset_cpus_allowed_locked(tsk);
+ mutex_unlock(&callback_mutex);
+
+ return mask;
+}
+
+/**
+ * cpuset_cpus_allowed_locked - return cpus_allowed mask from a tasks cpuset.
+ * Must be called with callback_mutex held.
+ **/
+cpumask_t cpuset_cpus_allowed_locked(struct task_struct *tsk)
+{
+ cpumask_t mask;
+
task_lock(tsk);
guarantee_online_cpus(task_cs(tsk), &mask);
task_unlock(tsk);
- mutex_unlock(&callback_mutex);
return mask;
}
diff -puN kernel/sched.c~hotplug-cpu-migrate-a-task-within-its-cpuset kernel/sched.c
--- a/kernel/sched.c~hotplug-cpu-migrate-a-task-within-its-cpuset
+++ a/kernel/sched.c
@@ -5145,8 +5145,16 @@ restart:
/* No more Mr. Nice Guy. */
if (dest_cpu == NR_CPUS) {
+ cpumask_t cpus_allowed = cpuset_cpus_allowed_locked();
+ /*
+ * Try to stay on the same cpuset, where the current cpuset
+ * may be a subset of all cpus.
+ * The cpuset_cpus_allowed_locked() variant of
+ * cpuset_cpus_allowed() will not block
+ * It must be called within calls to cpuset_lock/cpuset_unlock.
+ */
rq = task_rq_lock(p, &flags);
- cpus_setall(p->cpus_allowed);
+ p->cpus_allowed = cpus_allowed;
dest_cpu = any_online_cpu(p->cpus_allowed);
task_rq_unlock(rq, &flags);
@@ -5465,6 +5473,7 @@ migration_call(struct notifier_block *nf
case CPU_DEAD:
case CPU_DEAD_FROZEN:
+ cpuset_lock(); /* around calls to cpuset_cpus_allowed_lock() */
migrate_live_tasks(cpu);
rq = cpu_rq(cpu);
kthread_stop(rq->migration_thread);
@@ -5478,6 +5487,7 @@ migration_call(struct notifier_block *nf
rq->idle->sched_class = &idle_sched_class;
migrate_dead_tasks(cpu);
spin_unlock_irq(&rq->lock);
+ cpuset_unlock();
migrate_nr_uninterruptible(rq);
BUG_ON(rq->nr_running != 0);
_
Patches currently in -mm which might be from cpw@xxxxxxx are
do-cpu_dead-migrating-under-read_locktasklist-instead-of-write_lock_irqtasklist.patch
migration_callcpu_dead-use-spin_lock_irq-instead-of-task_rq_lock.patch
hotplug-cpu-migrate-a-task-within-its-cpuset.patch
hotplug-cpu-migrate-a-task-within-its-cpuset-doc.patch
-
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
