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rcu: priority boosting for TINY_PREEMPT_RCU

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Add priority boosting, but only for TINY_PREEMPT_RCU.  This is enabled
by the default-off RCU_BOOST kernel parameter.  The priority to which to
boost preempted RCU readers is controlled by the RCU_BOOST_PRIO kernel
parameter (defaulting to real-time priority 1) and the time to wait
before boosting the readers blocking a given grace period is controlled
by the RCU_BOOST_DELAY kernel parameter (defaulting to 500 milliseconds).

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
2010-09-27 17:25:23 -07:00
committed by Paul E. McKenney
parent b2c0710c46
commit 24278d1483
5 changed files with 280 additions and 53 deletions
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66
kernel/rcutiny.c
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@@ -36,38 +36,16 @@
#include <linux/time.h>
#include <linux/cpu.h>
/* Global control variables for rcupdate callback mechanism. */
struct rcu_ctrlblk {
struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
struct rcu_head **curtail; /* ->next pointer of last CB. */
};
/* Definition for rcupdate control block. */
static struct rcu_ctrlblk rcu_sched_ctrlblk = {
.donetail = &rcu_sched_ctrlblk.rcucblist,
.curtail = &rcu_sched_ctrlblk.rcucblist,
};
static struct rcu_ctrlblk rcu_bh_ctrlblk = {
.donetail = &rcu_bh_ctrlblk.rcucblist,
.curtail = &rcu_bh_ctrlblk.rcucblist,
};
#ifdef CONFIG_DEBUG_LOCK_ALLOC
int rcu_scheduler_active __read_mostly;
EXPORT_SYMBOL_GPL(rcu_scheduler_active);
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
/* Controls for rcu_cbs() kthread, replacing RCU_SOFTIRQ used previously. */
static struct task_struct *rcu_cbs_task;
static DECLARE_WAIT_QUEUE_HEAD(rcu_cbs_wq);
static unsigned long have_rcu_cbs;
static void invoke_rcu_cbs(void);
/* 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;
static void invoke_rcu_kthread(void);
/* Forward declarations for rcutiny_plugin.h. */
struct rcu_ctrlblk;
static void rcu_process_callbacks(struct rcu_ctrlblk *rcp);
static int rcu_cbs(void *arg);
static int rcu_kthread(void *arg);
static void __call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *rcu),
struct rcu_ctrlblk *rcp);
@@ -130,7 +108,7 @@ void rcu_sched_qs(int cpu)
{
if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
rcu_qsctr_help(&rcu_bh_ctrlblk))
invoke_rcu_cbs();
invoke_rcu_kthread();
}
/*
@@ -139,7 +117,7 @@ void rcu_sched_qs(int cpu)
void rcu_bh_qs(int cpu)
{
if (rcu_qsctr_help(&rcu_bh_ctrlblk))
invoke_rcu_cbs();
invoke_rcu_kthread();
}
/*
@@ -201,37 +179,41 @@ static void rcu_process_callbacks(struct rcu_ctrlblk *rcp)
* This is a kthread, but it is never stopped, at least not until
* the system goes down.
*/
static int rcu_cbs(void *arg)
static int rcu_kthread(void *arg)
{
unsigned long work;
unsigned long morework;
unsigned long flags;
for (;;) {
wait_event(rcu_cbs_wq, have_rcu_cbs != 0);
wait_event(rcu_kthread_wq, have_rcu_kthread_work != 0);
morework = rcu_boost();
local_irq_save(flags);
work = have_rcu_cbs;
have_rcu_cbs = 0;
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. */
}
/*
* Wake up rcu_cbs() to process callbacks now eligible for invocation.
* Wake up rcu_kthread() to process callbacks now eligible for invocation
* or to boost readers.
*/
static void invoke_rcu_cbs(void)
static void invoke_rcu_kthread(void)
{
unsigned long flags;
local_irq_save(flags);
have_rcu_cbs = 1;
wake_up(&rcu_cbs_wq);
have_rcu_kthread_work = 1;
wake_up(&rcu_kthread_wq);
local_irq_restore(flags);
}
@@ -327,7 +309,11 @@ EXPORT_SYMBOL_GPL(rcu_barrier_sched);
*/
static int __init rcu_spawn_kthreads(void)
{
rcu_cbs_task = kthread_run(rcu_cbs, NULL, "rcu_cbs");
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);