[PATCH UPDATED 2/4] sched: adjust when cpu_active and cpuset configurationsare updated during cpu on/offlining
From: Tejun Heo
Date: Wed Jun 02 2010 - 12:04:14 EST
Currently, when a cpu goes down, cpu_active is cleared before
CPU_DOWN_PREPARE starts and cpuset configuration is updated from a
default priority cpu notifier. When a cpu is coming up, it's set
before CPU_ONLINE but cpuset configuration again is updated from the
same cpu notifier.
For cpu notifiers, this presents an inconsistent state. Threads which
a CPU_DOWN_PREPARE notifier expects to be bound to the CPU can be
migrated to other cpus because the cpu is no more inactive.
Fix it by updating cpu_active in the highest priority cpu notifier and
cpuset configuration in the second highest when a cpu is coming up.
Down path is updated similarly. This guarantees that all other cpu
notifiers see consistent cpu_active and cpuset configuration.
cpuset_track_online_cpus() notifier is converted to
cpuset_update_active_cpus() which just updates the configuration and
now called from cpuset_cpu_[in]active() notifiers registered from
sched_init_smp(). If cpuset is disabled, cpuset_update_active_cpus()
degenerates into partition_sched_domains() making separate notifier
for !CONFIG_CPUSETS unnecessary.
This problem is triggered by cmwq. During CPU_DOWN_PREPARE, hotplug
callback creates a kthread and kthread_bind()s it to the target cpu,
and the thread is expected to run on that cpu.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Paul Menage <menage@xxxxxxxxxx>
---
Okay, how about this one? Using notifiers seems better for the
following reasons.
* Rollback on failure.
* cpuset/sched_domain don't expect to be called before smp
configuration is complete. If hardcoded into cpu_up/down(),
condition checks need to be added so that they're skipped if the
system is bringing up the cpus for the first time.
Works fine here w/ CPUSET enabled and disabled.
Thanks.
include/linux/cpu.h | 16 +++++++++++
include/linux/cpuset.h | 6 ++++
kernel/cpu.c | 6 ----
kernel/cpuset.c | 21 +--------------
kernel/sched.c | 67 ++++++++++++++++++++++++++++++++++++-------------
5 files changed, 74 insertions(+), 42 deletions(-)
Index: work/include/linux/cpu.h
===================================================================
--- work.orig/include/linux/cpu.h
+++ work/include/linux/cpu.h
@@ -52,6 +52,22 @@ struct notifier_block;
* CPU notifier priorities.
*/
enum {
+ /*
+ * SCHED_ACTIVE marks a cpu which is coming up active during
+ * CPU_ONLINE and CPU_DOWN_FAILED and must be the first
+ * notifier. CPUSET_ACTIVE adjusts cpuset according to
+ * cpu_active mask right after SCHED_ACTIVE. During
+ * CPU_DOWN_PREPARE, SCHED_INACTIVE and CPUSET_INACTIVE are
+ * ordered in the similar way.
+ *
+ * This ordering guarantees consistent cpu_active mask and
+ * migration behavior to all cpu notifiers.
+ */
+ CPU_PRI_SCHED_ACTIVE = INT_MAX,
+ CPU_PRI_CPUSET_ACTIVE = INT_MAX - 1,
+ CPU_PRI_SCHED_INACTIVE = INT_MIN + 1,
+ CPU_PRI_CPUSET_INACTIVE = INT_MIN,
+
/* migration should happen before other stuff but after perf */
CPU_PRI_PERF = 20,
CPU_PRI_MIGRATION = 10,
Index: work/kernel/cpu.c
===================================================================
--- work.orig/kernel/cpu.c
+++ work/kernel/cpu.c
@@ -211,12 +211,9 @@ static int __ref _cpu_down(unsigned int
return -EINVAL;
cpu_hotplug_begin();
- set_cpu_active(cpu, false);
err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
hcpu, -1, &nr_calls);
if (err == NOTIFY_BAD) {
- set_cpu_active(cpu, true);
-
nr_calls--;
__raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
hcpu, nr_calls, NULL);
@@ -228,7 +225,6 @@ static int __ref _cpu_down(unsigned int
err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
if (err) {
- set_cpu_active(cpu, true);
/* CPU didn't die: tell everyone. Can't complain. */
if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
hcpu) == NOTIFY_BAD)
@@ -309,8 +305,6 @@ static int __cpuinit _cpu_up(unsigned in
goto out_notify;
BUG_ON(!cpu_online(cpu));
- set_cpu_active(cpu, true);
-
/* Now call notifier in preparation. */
raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
Index: work/kernel/cpuset.c
===================================================================
--- work.orig/kernel/cpuset.c
+++ work/kernel/cpuset.c
@@ -2071,31 +2071,17 @@ static void scan_for_empty_cpusets(struc
* but making no active use of cpusets.
*
* This routine ensures that top_cpuset.cpus_allowed tracks
- * cpu_online_map on each CPU hotplug (cpuhp) event.
+ * cpu_active_mask on each CPU hotplug (cpuhp) event.
*
* Called within get_online_cpus(). Needs to call cgroup_lock()
* before calling generate_sched_domains().
*/
-static int cpuset_track_online_cpus(struct notifier_block *unused_nb,
- unsigned long phase, void *unused_cpu)
+void cpuset_update_active_cpus(void)
{
struct sched_domain_attr *attr;
cpumask_var_t *doms;
int ndoms;
- switch (phase) {
- case CPU_ONLINE:
- case CPU_ONLINE_FROZEN:
- case CPU_DOWN_PREPARE:
- case CPU_DOWN_PREPARE_FROZEN:
- case CPU_DOWN_FAILED:
- case CPU_DOWN_FAILED_FROZEN:
- break;
-
- default:
- return NOTIFY_DONE;
- }
-
cgroup_lock();
mutex_lock(&callback_mutex);
cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
@@ -2106,8 +2092,6 @@ static int cpuset_track_online_cpus(stru
/* Have scheduler rebuild the domains */
partition_sched_domains(ndoms, doms, attr);
-
- return NOTIFY_OK;
}
#ifdef CONFIG_MEMORY_HOTPLUG
@@ -2161,7 +2145,6 @@ void __init cpuset_init_smp(void)
cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
- hotcpu_notifier(cpuset_track_online_cpus, 0);
hotplug_memory_notifier(cpuset_track_online_nodes, 10);
cpuset_wq = create_singlethread_workqueue("cpuset");
Index: work/kernel/sched.c
===================================================================
--- work.orig/kernel/sched.c
+++ work/kernel/sched.c
@@ -5840,17 +5840,46 @@ static struct notifier_block __cpuinitda
.priority = CPU_PRI_MIGRATION,
};
+static int __cpuinit sched_cpu_active(struct notifier_block *nfb,
+ unsigned long action, void *hcpu)
+{
+ switch (action & ~CPU_TASKS_FROZEN) {
+ case CPU_ONLINE:
+ case CPU_DOWN_FAILED:
+ set_cpu_active((long)hcpu, true);
+ return NOTIFY_OK;
+ default:
+ return NOTIFY_DONE;
+ }
+}
+
+static int __cpuexit sched_cpu_inactive(struct notifier_block *nfb,
+ unsigned long action, void *hcpu)
+{
+ switch (action & ~CPU_TASKS_FROZEN) {
+ case CPU_DOWN_PREPARE:
+ set_cpu_active((long)hcpu, false);
+ return NOTIFY_OK;
+ default:
+ return NOTIFY_DONE;
+ }
+}
+
static int __init migration_init(void)
{
void *cpu = (void *)(long)smp_processor_id();
int err;
- /* Start one for the boot CPU: */
+ /* Initialize migration for the boot CPU */
err = migration_call(&migration_notifier, CPU_UP_PREPARE, cpu);
BUG_ON(err == NOTIFY_BAD);
migration_call(&migration_notifier, CPU_ONLINE, cpu);
register_cpu_notifier(&migration_notifier);
+ /* Register cpu active notifiers */
+ cpu_notifier(sched_cpu_active, CPU_PRI_SCHED_ACTIVE);
+ cpu_notifier(sched_cpu_inactive, CPU_PRI_SCHED_INACTIVE);
+
return 0;
}
early_initcall(migration_init);
@@ -7309,29 +7338,35 @@ int __init sched_create_sysfs_power_savi
}
#endif /* CONFIG_SCHED_MC || CONFIG_SCHED_SMT */
-#ifndef CONFIG_CPUSETS
/*
- * Add online and remove offline CPUs from the scheduler domains.
- * When cpusets are enabled they take over this function.
+ * Update cpusets according to cpu_active mask. If cpusets are
+ * disabled, cpuset_update_active_cpus() becomes a simple wrapper
+ * around partition_sched_domains().
*/
-static int update_sched_domains(struct notifier_block *nfb,
- unsigned long action, void *hcpu)
+static int __cpuinit cpuset_cpu_active(struct notifier_block *nfb,
+ unsigned long action, void *hcpu)
{
- switch (action) {
+ switch (action & ~CPU_TASKS_FROZEN) {
case CPU_ONLINE:
- case CPU_ONLINE_FROZEN:
- case CPU_DOWN_PREPARE:
- case CPU_DOWN_PREPARE_FROZEN:
case CPU_DOWN_FAILED:
- case CPU_DOWN_FAILED_FROZEN:
- partition_sched_domains(1, NULL, NULL);
+ cpuset_update_active_cpus();
return NOTIFY_OK;
+ default:
+ return NOTIFY_DONE;
+ }
+}
+static int __cpuexit cpuset_cpu_inactive(struct notifier_block *nfb,
+ unsigned long action, void *hcpu)
+{
+ switch (action & ~CPU_TASKS_FROZEN) {
+ case CPU_DOWN_PREPARE:
+ cpuset_update_active_cpus();
+ return NOTIFY_OK;
default:
return NOTIFY_DONE;
}
}
-#endif
static int update_runtime(struct notifier_block *nfb,
unsigned long action, void *hcpu)
@@ -7377,10 +7412,8 @@ void __init sched_init_smp(void)
mutex_unlock(&sched_domains_mutex);
put_online_cpus();
-#ifndef CONFIG_CPUSETS
- /* XXX: Theoretical race here - CPU may be hotplugged now */
- hotcpu_notifier(update_sched_domains, 0);
-#endif
+ hotcpu_notifier(cpuset_cpu_active, CPU_PRI_CPUSET_ACTIVE);
+ hotcpu_notifier(cpuset_cpu_inactive, CPU_PRI_CPUSET_INACTIVE);
/* RT runtime code needs to handle some hotplug events */
hotcpu_notifier(update_runtime, 0);
Index: work/include/linux/cpuset.h
===================================================================
--- work.orig/include/linux/cpuset.h
+++ work/include/linux/cpuset.h
@@ -20,6 +20,7 @@ extern int number_of_cpusets; /* How man
extern int cpuset_init(void);
extern void cpuset_init_smp(void);
+extern void cpuset_update_active_cpus(void);
extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
extern int cpuset_cpus_allowed_fallback(struct task_struct *p);
extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
@@ -96,6 +97,11 @@ static inline void set_mems_allowed(node
static inline int cpuset_init(void) { return 0; }
static inline void cpuset_init_smp(void) {}
+static inline void cpuset_update_active_cpus(void)
+{
+ partition_sched_domains(1, NULL, NULL);
+}
+
static inline void cpuset_cpus_allowed(struct task_struct *p,
struct cpumask *mask)
{
--
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