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rcu: use softirq instead of kthreads except when RCU_BOOST=y

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This patch #ifdefs RCU kthreads out of the kernel unless RCU_BOOST=y,
thus eliminating context-switch overhead if RCU priority boosting has
not been configured.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney
2011-06-15 15:47:09 -07:00
parent 09223371de
commit a46e0899ee
4 changed files with 99 additions and 41 deletions
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59
kernel/rcutree.c
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@@ -87,6 +87,8 @@ static struct rcu_state *rcu_state;
int rcu_scheduler_active __read_mostly;
EXPORT_SYMBOL_GPL(rcu_scheduler_active);
#ifdef CONFIG_RCU_BOOST
/*
* Control variables for per-CPU and per-rcu_node kthreads. These
* handle all flavors of RCU.
@@ -98,9 +100,11 @@ DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
DEFINE_PER_CPU(char, rcu_cpu_has_work);
static char rcu_kthreads_spawnable;
#endif /* #ifdef CONFIG_RCU_BOOST */
static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
static void invoke_rcu_cpu_kthread(void);
static void __invoke_rcu_cpu_kthread(void);
static void invoke_rcu_core(void);
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
#define RCU_KTHREAD_PRIO 1 /* RT priority for per-CPU kthreads. */
@@ -1089,6 +1093,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
int need_report = 0;
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_node *rnp;
#ifdef CONFIG_RCU_BOOST
struct task_struct *t;
/* Stop the CPU's kthread. */
@@ -1097,6 +1102,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
per_cpu(rcu_cpu_kthread_task, cpu) = NULL;
kthread_stop(t);
}
#endif /* #ifdef CONFIG_RCU_BOOST */
/* Exclude any attempts to start a new grace period. */
raw_spin_lock_irqsave(&rsp->onofflock, flags);
@@ -1232,7 +1238,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
/* Re-raise the RCU softirq if there are callbacks remaining. */
if (cpu_has_callbacks_ready_to_invoke(rdp))
invoke_rcu_cpu_kthread();
invoke_rcu_core();
}
/*
@@ -1278,7 +1284,7 @@ void rcu_check_callbacks(int cpu, int user)
}
rcu_preempt_check_callbacks(cpu);
if (rcu_pending(cpu))
invoke_rcu_cpu_kthread();
invoke_rcu_core();
}
#ifdef CONFIG_SMP
@@ -1444,9 +1450,11 @@ __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
/* If there are callbacks ready, invoke them. */
if (cpu_has_callbacks_ready_to_invoke(rdp))
__invoke_rcu_cpu_kthread();
invoke_rcu_callbacks(rsp, rdp);
}
#ifdef CONFIG_RCU_BOOST
static void rcu_kthread_do_work(void)
{
rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
@@ -1454,6 +1462,8 @@ static void rcu_kthread_do_work(void)
rcu_preempt_do_callbacks();
}
#endif /* #ifdef CONFIG_RCU_BOOST */
/*
* Do softirq processing for the current CPU.
*/
@@ -1474,25 +1484,22 @@ static void rcu_process_callbacks(struct softirq_action *unused)
* the current CPU with interrupts disabled, the rcu_cpu_kthread_task
* cannot disappear out from under us.
*/
static void __invoke_rcu_cpu_kthread(void)
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
{
unsigned long flags;
local_irq_save(flags);
__this_cpu_write(rcu_cpu_has_work, 1);
if (__this_cpu_read(rcu_cpu_kthread_task) == NULL) {
local_irq_restore(flags);
if (likely(!rsp->boost)) {
rcu_do_batch(rsp, rdp);
return;
}
wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
local_irq_restore(flags);
invoke_rcu_callbacks_kthread();
}
static void invoke_rcu_cpu_kthread(void)
static void invoke_rcu_core(void)
{
raise_softirq(RCU_SOFTIRQ);
}
#ifdef CONFIG_RCU_BOOST
/*
* Wake up the specified per-rcu_node-structure kthread.
* Because the per-rcu_node kthreads are immortal, we don't need
@@ -1818,6 +1825,18 @@ static int __init rcu_spawn_kthreads(void)
}
early_initcall(rcu_spawn_kthreads);
#else /* #ifdef CONFIG_RCU_BOOST */
static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
{
}
static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
{
}
#endif /* #else #ifdef CONFIG_RCU_BOOST */
static void
__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
struct rcu_state *rsp)
@@ -2224,6 +2243,8 @@ static void __cpuinit rcu_prepare_cpu(int cpu)
rcu_preempt_init_percpu_data(cpu);
}
#ifdef CONFIG_RCU_BOOST
static void __cpuinit rcu_prepare_kthreads(int cpu)
{
struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
@@ -2237,6 +2258,14 @@ static void __cpuinit rcu_prepare_kthreads(int cpu)
}
}
#else /* #ifdef CONFIG_RCU_BOOST */
static void __cpuinit rcu_prepare_kthreads(int cpu)
{
}
#endif /* #else #ifdef CONFIG_RCU_BOOST */
/*
* Handle CPU online/offline notification events.
*/