On Thu, Jan 31, 2013 at 12:11:19PM -0000, Thomas Gleixner wrote:
> The scheduler sports quite a bunch of hotplug notifiers. One reason
> for multiple notifiers is the fact, that the startup and teardown
> process are asymetric. Now the scheduler wants to be called early on
> startup and late on teardown. That requires to install two different
> notifiers for the same issue.
>
> With the state machine implementation we can register a callback pair
> for startup and teardown at the appropriate spot.
>
> This patch converts the notifiers which are setup with special
> priorities and combines CPU_PRI_SCHED and CPU_PRI_CPUSET notifiers to
> a single callback. They run back to back anyway and we can make sure
> in the callbacks that the ordering inside the scheduler is
> correct. These notifiers are installed in sched_init_smp() as we can't
> run them during the bringup of the non boot cpus because the smp
> scheduler is setup after that. It would be nice if we just could
> compile them in, but that needs a larger surgery to the scheduler code
> and is beyond the scope of this patch.
>
> Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Reviewed-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> ---
> include/linux/cpu.h | 16 ----
> include/linux/cpuhotplug.h | 6 +
> kernel/cpu.c | 4 +
> kernel/sched/core.c | 154
> +++++++++++++++++----------------------------
> 4 files changed, 69 insertions(+), 111 deletions(-)
>
> Index: linux-2.6/include/linux/cpu.h
> ===================================================================
> --- linux-2.6.orig/include/linux/cpu.h
> +++ linux-2.6/include/linux/cpu.h
> @@ -58,22 +58,6 @@ extern ssize_t arch_print_cpu_modalias(s
> * 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: linux-2.6/include/linux/cpuhotplug.h
> ===================================================================
> --- linux-2.6.orig/include/linux/cpuhotplug.h
> +++ linux-2.6/include/linux/cpuhotplug.h
> @@ -6,13 +6,16 @@ enum cpuhp_states {
> CPUHP_CREATE_THREADS,
> CPUHP_NOTIFY_PREPARE,
> CPUHP_NOTIFY_DEAD,
> + CPUHP_SCHED_DEAD,
> CPUHP_BRINGUP_CPU,
> CPUHP_AP_OFFLINE,
> + CPUHP_AP_SCHED_STARTING,
> CPUHP_AP_NOTIFY_STARTING,
> CPUHP_AP_NOTIFY_DYING,
> CPUHP_AP_MAX,
> CPUHP_TEARDOWN_CPU,
> CPUHP_PERCPU_THREADS,
> + CPUHP_SCHED_ONLINE,
> CPUHP_NOTIFY_ONLINE,
> CPUHP_NOTIFY_DOWN_PREPARE,
> CPUHP_MAX,
> @@ -87,4 +90,7 @@ static inline void cpuhp_remove_state_no
> __cpuhp_remove_state(state, false);
> }
>
> +/* Compiled in scheduler hotplug functions */
> +int sched_starting_cpu(unsigned int cpu);
> +
> #endif
> Index: linux-2.6/kernel/cpu.c
> ===================================================================
> --- linux-2.6.orig/kernel/cpu.c
> +++ linux-2.6/kernel/cpu.c
> @@ -788,6 +788,10 @@ static struct cpuhp_step cpuhp_bp_states
> /* Application processor state steps */
> static struct cpuhp_step cpuhp_ap_states[] = {
> #ifdef CONFIG_SMP
> + [CPUHP_AP_SCHED_STARTING] = {
> + .startup = sched_starting_cpu,
> + .teardown = NULL,
> + },
> [CPUHP_AP_NOTIFY_STARTING] = {
> .startup = notify_starting,
> .teardown = NULL,
> Index: linux-2.6/kernel/sched/core.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched/core.c
> +++ linux-2.6/kernel/sched/core.c
> @@ -5167,31 +5167,6 @@ 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_STARTING:
> - case CPU_DOWN_FAILED:
> - set_cpu_active((long)hcpu, true);
> - return NOTIFY_OK;
> - default:
> - return NOTIFY_DONE;
> - }
> -}
> -
> -static int __cpuinit 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();
> @@ -5203,10 +5178,6 @@ static int __init migration_init(void)
> 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);
> @@ -6292,42 +6263,12 @@ static void sched_domains_numa_masks_cle
> }
> }
>
> -/*
> - * Update sched_domains_numa_masks[level][node] array when new cpus
> - * are onlined.
> - */
> -static int sched_domains_numa_masks_update(struct notifier_block *nfb,
> - unsigned long action,
> - void *hcpu)
> -{
> - int cpu = (long)hcpu;
> -
> - switch (action & ~CPU_TASKS_FROZEN) {
> - case CPU_ONLINE:
> - sched_domains_numa_masks_set(cpu);
> - break;
> -
> - case CPU_DEAD:
> - sched_domains_numa_masks_clear(cpu);
> - break;
> -
> - default:
> - return NOTIFY_DONE;
> - }
> -
> - return NOTIFY_OK;
> -}
> #else
> -static inline void sched_init_numa(void)
> -{
> -}
> -
> -static int sched_domains_numa_masks_update(struct notifier_block *nfb,
> - unsigned long action,
> - void *hcpu)
> -{
> - return 0;
> -}
> +static inline void sched_init_numa(void) { }
> +#ifdef CONFIG_HOTPLUG_CPU
> +static void sched_domains_numa_masks_set(int cpu) { }
> +static void sched_domains_numa_masks_clear(int cpu) { }
> +#endif
> #endif /* CONFIG_NUMA */
>
> static int __sdt_alloc(const struct cpumask *cpu_map)
> @@ -6696,6 +6637,7 @@ match2:
> mutex_unlock(&sched_domains_mutex);
> }
>
> +#ifdef CONFIG_HOTPLUG_CPU
> static int num_cpus_frozen; /* used to mark begin/end of suspend/resume */
>
> /*
> @@ -6706,13 +6648,9 @@ static int num_cpus_frozen; /* used to m
> * If we come here as part of a suspend/resume, don't touch cpusets because
> we
> * want to restore it back to its original state upon resume anyway.
> */
> -static int cpuset_cpu_active(struct notifier_block *nfb, unsigned long
> action,
> - void *hcpu)
> +static void cpuset_cpu_active(void)
> {
> - switch (action) {
> - case CPU_ONLINE_FROZEN:
> - case CPU_DOWN_FAILED_FROZEN:
> -
> + if (cpuhp_tasks_frozen) {
> /*
> * num_cpus_frozen tracks how many CPUs are involved in suspend
> * resume sequence. As long as this is not the last online
> @@ -6722,40 +6660,62 @@ static int cpuset_cpu_active(struct noti
> num_cpus_frozen--;
> if (likely(num_cpus_frozen)) {
> partition_sched_domains(1, NULL, NULL);
> - break;
> + return;
> }
> -
> /*
> * This is the last CPU online operation. So fall through and
> * restore the original sched domains by considering the
> * cpuset configurations.
> */
> -
> - case CPU_ONLINE:
> - case CPU_DOWN_FAILED:
> - cpuset_update_active_cpus(true);
> - break;
> - default:
> - return NOTIFY_DONE;
> }
> - return NOTIFY_OK;
> + cpuset_update_active_cpus(true);
> }
>
> -static int cpuset_cpu_inactive(struct notifier_block *nfb, unsigned long
> action,
> - void *hcpu)
> +static void cpuset_cpu_inactive(void)
> {
> - switch (action) {
> - case CPU_DOWN_PREPARE:
> - cpuset_update_active_cpus(false);
> - break;
> - case CPU_DOWN_PREPARE_FROZEN:
> + if (cpuhp_tasks_frozen) {
> num_cpus_frozen++;
> partition_sched_domains(1, NULL, NULL);
> - break;
> - default:
> - return NOTIFY_DONE;
> - }
> - return NOTIFY_OK;
> + } else
> + cpuset_update_active_cpus(false);
> +}
> +
> +static int sched_dead_cpu(unsigned int cpu)
> +{
> + sched_domains_numa_masks_clear(cpu);
> + return 0;
> +}
> +
> +static int sched_online_cpu(unsigned int cpu)
> +{
> + /* Looks redundant, but we need it in case of down canceled */
> + set_cpu_active(cpu, true);
> + /*
> + * Asymetric to sched_dead_cpu, but this just fiddles with
> + * bits. Sigh
> + */
> + sched_domains_numa_masks_set(cpu);
> + /* This is actually symetric */
> + cpuset_cpu_active();
> + return 0;
> +}
> +
> +static int sched_offline_cpu(unsigned int cpu)
> +{
> + set_cpu_active(cpu, false);
> + cpuset_cpu_inactive();
> + return 0;
> +}
> +#else
> +#define sched_dead_cpu NULL
> +#define sched_online_cpu NULL
> +#define sched_offline_cpu NULL
> +#endif
> +
> +int __cpuinit sched_starting_cpu(unsigned int cpu)
> +{
> + set_cpu_active(cpu, true);
> + return 0;
> }
>
> void __init sched_init_smp(void)
> @@ -6776,9 +6736,13 @@ void __init sched_init_smp(void)
> mutex_unlock(&sched_domains_mutex);
> put_online_cpus();
>
> - hotcpu_notifier(sched_domains_numa_masks_update, CPU_PRI_SCHED_ACTIVE);
> - hotcpu_notifier(cpuset_cpu_active, CPU_PRI_CPUSET_ACTIVE);
> - hotcpu_notifier(cpuset_cpu_inactive, CPU_PRI_CPUSET_INACTIVE);
> + /*
> + * Note: These callbacks are installed late because we init
> + * numa and sched domains after we brought up the cpus.
> + */
> + cpuhp_setup_state_nocalls(CPUHP_SCHED_DEAD, NULL, sched_dead_cpu);
> + cpuhp_setup_state_nocalls(CPUHP_SCHED_ONLINE, sched_online_cpu,
> + sched_offline_cpu);
>
> /* RT runtime code needs to handle some hotplug events */
> hotcpu_notifier(update_runtime, 0);
>
>
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