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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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74
kernel/rcutiny.c
View file

@ -43,16 +43,11 @@
#include "rcu.h"
/* Controls for rcu_kthread() kthread, replacing RCU_SOFTIRQ used previously. */
static struct task_struct *rcu_kthread_task;
static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
static unsigned long have_rcu_kthread_work;
/* Forward declarations for rcutiny_plugin.h. */
struct rcu_ctrlblk;
static void invoke_rcu_kthread(void);
static void rcu_process_callbacks(struct rcu_ctrlblk *rcp);
static int rcu_kthread(void *arg);
static void invoke_rcu_callbacks(void);
static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
static void rcu_process_callbacks(struct softirq_action *unused);
static void __call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *rcu),
struct rcu_ctrlblk *rcp);
@ -101,16 +96,6 @@ static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
return 0;
}
/*
* Wake up rcu_kthread() to process callbacks now eligible for invocation
* or to boost readers.
*/
static void invoke_rcu_kthread(void)
{
have_rcu_kthread_work = 1;
wake_up(&rcu_kthread_wq);
}
/*
* Record an rcu quiescent state. And an rcu_bh quiescent state while we
* are at it, given that any rcu quiescent state is also an rcu_bh
@ -123,7 +108,7 @@ void rcu_sched_qs(int cpu)
local_irq_save(flags);
if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
rcu_qsctr_help(&rcu_bh_ctrlblk))
invoke_rcu_kthread();
invoke_rcu_callbacks();
local_irq_restore(flags);
}
@ -136,7 +121,7 @@ void rcu_bh_qs(int cpu)
local_irq_save(flags);
if (rcu_qsctr_help(&rcu_bh_ctrlblk))
invoke_rcu_kthread();
invoke_rcu_callbacks();
local_irq_restore(flags);
}
@ -160,7 +145,7 @@ void rcu_check_callbacks(int cpu, int user)
* Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
* whose grace period has elapsed.
*/
static void rcu_process_callbacks(struct rcu_ctrlblk *rcp)
static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
{
struct rcu_head *next, *list;
unsigned long flags;
@ -200,36 +185,11 @@ static void rcu_process_callbacks(struct rcu_ctrlblk *rcp)
RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count));
}
/*
* This kthread invokes RCU callbacks whose grace periods have
* elapsed. It is awakened as needed, and takes the place of the
* RCU_SOFTIRQ that was used previously for this purpose.
* This is a kthread, but it is never stopped, at least not until
* the system goes down.
*/
static int rcu_kthread(void *arg)
static void rcu_process_callbacks(struct softirq_action *unused)
{
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(&rcu_sched_ctrlblk);
rcu_process_callbacks(&rcu_bh_ctrlblk);
rcu_preempt_process_callbacks();
}
schedule_timeout_interruptible(1); /* Leave CPU for others. */
}
return 0; /* Not reached, but needed to shut gcc up. */
__rcu_process_callbacks(&rcu_sched_ctrlblk);
__rcu_process_callbacks(&rcu_bh_ctrlblk);
rcu_preempt_process_callbacks();
}
/*
@ -291,17 +251,3 @@ void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
__call_rcu(head, func, &rcu_bh_ctrlblk);
}
EXPORT_SYMBOL_GPL(call_rcu_bh);
/*
* 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);