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rcu: Make TINY_RCU also use softirq for RCU_BOOST=n

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This patch #ifdefs TINY_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 <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2011-06-18 09:55:39 -07:00 • committed by Paul E. McKenney
parent 385680a948
commit 965a002b4f
3 changed files with 97 additions and 91 deletions
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110
kernel/rcutiny_plugin.h
View file

@ -245,6 +245,13 @@ static void show_tiny_preempt_stats(struct seq_file *m)
#include "rtmutex_common.h"
#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
/* Controls for rcu_kthread() kthread. */
static struct task_struct *rcu_kthread_task;
static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
static unsigned long have_rcu_kthread_work;
/*
* Carry out RCU priority boosting on the task indicated by ->boost_tasks,
* and advance ->boost_tasks to the next task in the ->blkd_tasks list.
@ -332,7 +339,7 @@ static int rcu_initiate_boost(void)
if (rcu_preempt_ctrlblk.exp_tasks == NULL)
rcu_preempt_ctrlblk.boost_tasks =
rcu_preempt_ctrlblk.gp_tasks;
invoke_rcu_kthread();
invoke_rcu_callbacks();
} else
RCU_TRACE(rcu_initiate_boost_trace());
return 1;
@ -350,14 +357,6 @@ static void rcu_preempt_boost_start_gp(void)
#else /* #ifdef CONFIG_RCU_BOOST */
/*
* If there is no RCU priority boosting, we don't boost.
*/
static int rcu_boost(void)
{
return 0;
}
/*
* If there is no RCU priority boosting, we don't initiate boosting,
* but we do indicate whether there are blocked readers blocking the
@ -425,7 +424,7 @@ static void rcu_preempt_cpu_qs(void)
/* If there are done callbacks, cause them to be invoked. */
if (*rcu_preempt_ctrlblk.rcb.donetail != NULL)
invoke_rcu_kthread();
invoke_rcu_callbacks();
}
/*
@ -646,7 +645,7 @@ static void rcu_preempt_check_callbacks(void)
rcu_preempt_cpu_qs();
if (&rcu_preempt_ctrlblk.rcb.rcucblist !=
rcu_preempt_ctrlblk.rcb.donetail)
invoke_rcu_kthread();
invoke_rcu_callbacks();
if (rcu_preempt_gp_in_progress() &&
rcu_cpu_blocking_cur_gp() &&
rcu_preempt_running_reader())
@ -672,7 +671,7 @@ static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
*/
static void rcu_preempt_process_callbacks(void)
{
rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb);
__rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb);
}
/*
@ -847,15 +846,6 @@ static void show_tiny_preempt_stats(struct seq_file *m)
#endif /* #ifdef CONFIG_RCU_TRACE */
/*
* Because preemptible RCU does not exist, it is never necessary to
* boost preempted RCU readers.
*/
static int rcu_boost(void)
{
return 0;
}
/*
* Because preemptible RCU does not exist, it never has any callbacks
* to check.
@ -882,6 +872,78 @@ static void rcu_preempt_process_callbacks(void)
#endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */
#ifdef CONFIG_RCU_BOOST
/*
* Wake up rcu_kthread() to process callbacks now eligible for invocation
* or to boost readers.
*/
static void invoke_rcu_callbacks(void)
{
have_rcu_kthread_work = 1;
wake_up(&rcu_kthread_wq);
}
/*
* This kthread invokes RCU callbacks whose grace periods have
* elapsed. It is awakened as needed, and takes the place of the
* RCU_SOFTIRQ that is used for this purpose when boosting is disabled.
* This is a kthread, but it is never stopped, at least not until
* the system goes down.
*/
static int rcu_kthread(void *arg)
{
unsigned long work;
unsigned long morework;
unsigned long flags;
for (;;) {
wait_event_interruptible(rcu_kthread_wq,
have_rcu_kthread_work != 0);
morework = rcu_boost();
local_irq_save(flags);
work = have_rcu_kthread_work;
have_rcu_kthread_work = morework;
local_irq_restore(flags);
if (work)
rcu_process_callbacks(NULL);
schedule_timeout_interruptible(1); /* Leave CPU for others. */
}
return 0; /* Not reached, but needed to shut gcc up. */
}
/*
* Spawn the kthread that invokes RCU callbacks.
*/
static int __init rcu_spawn_kthreads(void)
{
struct sched_param sp;
rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread");
sp.sched_priority = RCU_BOOST_PRIO;
sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp);
return 0;
}
early_initcall(rcu_spawn_kthreads);
#else /* #ifdef CONFIG_RCU_BOOST */
/*
* Start up softirq processing of callbacks.
*/
void invoke_rcu_callbacks(void)
{
raise_softirq(RCU_SOFTIRQ);
}
void rcu_init(void)
{
open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
}
#endif /* #else #ifdef CONFIG_RCU_BOOST */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
#include <linux/kernel_stat.h>
@ -897,12 +959,6 @@ void __init rcu_scheduler_starting(void)
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
#ifdef CONFIG_RCU_BOOST
#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
#else /* #ifdef CONFIG_RCU_BOOST */
#define RCU_BOOST_PRIO 1
#endif /* #else #ifdef CONFIG_RCU_BOOST */
#ifdef CONFIG_RCU_TRACE
#ifdef CONFIG_RCU_BOOST