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Message-ID: <20070824221806.GA3602@sgi.com>
Date: Fri, 24 Aug 2007 17:18:06 -0500
From: Cliff Wickman <cpw@....com>
To: akpm@...ux-foundation.org, ego@...ibm.com, mingo@...e.hu,
vatsa@...ibm.com, oleg@...sign.ru, pj@....com
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH 1/1] hotplug cpu: migrate a task within its cpuset
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_lock(), a new variant of cpuset_cpus_allowed() that
will not block.
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()
Diffed against 2.6.23-rc3
Signed-off-by: Cliff Wickman <cpw@....com>
---
include/linux/cpuset.h | 5 +++++
kernel/cpuset.c | 19 +++++++++++++++++++
kernel/sched.c | 14 ++++++++++++++
3 files changed, 38 insertions(+)
Index: linus.070821/kernel/sched.c
===================================================================
--- linus.070821.orig/kernel/sched.c
+++ linus.070821/kernel/sched.c
@@ -61,6 +61,7 @@
#include <linux/delayacct.h>
#include <linux/reciprocal_div.h>
#include <linux/unistd.h>
+#include <linux/cpuset.h>
#include <asm/tlb.h>
@@ -5091,6 +5092,17 @@ restart:
if (dest_cpu == NR_CPUS)
dest_cpu = any_online_cpu(p->cpus_allowed);
+ /* try to stay on the same cpuset */
+ if (dest_cpu == NR_CPUS) {
+ /*
+ * The cpuset_cpus_allowed_lock() variant of
+ * cpuset_cpus_allowed() will not block
+ * It must be called within calls to cpuset_lock/cpuset_unlock.
+ */
+ p->cpus_allowed = cpuset_cpus_allowed_lock(p);
+ dest_cpu = any_online_cpu(p->cpus_allowed);
+ }
+
/* No more Mr. Nice Guy. */
if (dest_cpu == NR_CPUS) {
rq = task_rq_lock(p, &flags);
@@ -5412,6 +5424,7 @@ 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);
@@ -5425,6 +5438,7 @@ 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);
Index: linus.070821/include/linux/cpuset.h
===================================================================
--- linus.070821.orig/include/linux/cpuset.h
+++ linus.070821/include/linux/cpuset.h
@@ -22,6 +22,7 @@ extern void cpuset_init_smp(void);
extern void cpuset_fork(struct task_struct *p);
extern void cpuset_exit(struct task_struct *p);
extern cpumask_t cpuset_cpus_allowed(struct task_struct *p);
+extern cpumask_t cpuset_cpus_allowed_lock(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);
@@ -87,6 +88,10 @@ static inline cpumask_t cpuset_cpus_allo
{
return cpu_possible_map;
}
+static inline cpumask_t cpuset_cpus_allowed_lock(struct task_struct *p)
+{
+ return cpu_possible_map;
+}
static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
{
Index: linus.070821/kernel/cpuset.c
===================================================================
--- linus.070821.orig/kernel/cpuset.c
+++ linus.070821/kernel/cpuset.c
@@ -2333,6 +2333,25 @@ cpumask_t cpuset_cpus_allowed(struct tas
return mask;
}
+/**
+ * cpuset_cpus_allowed_lock - return cpus_allowed mask from a tasks cpuset.
+ * @tsk: pointer to task_struct from which to obtain cpuset->cpus_allowed.
+ *
+ * Description: Same as cpuset_cpus_allowed, but called with callback_mutex
+ * already held.
+ **/
+
+cpumask_t cpuset_cpus_allowed_lock(struct task_struct *tsk)
+{
+ cpumask_t mask;
+
+ task_lock(tsk);
+ guarantee_online_cpus(tsk->cpuset, &mask);
+ task_unlock(tsk);
+
+ return mask;
+}
+
void cpuset_init_current_mems_allowed(void)
{
current->mems_allowed = NODE_MASK_ALL;
--
Cliff Wickman
Silicon Graphics, Inc.
cpw@....com
(651) 683-3824
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