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rcu: priority boosting for TINY_PREEMPT_RCU 

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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
include/linux/init_task.h
View File

@ -81,6 +81,12 @@ extern struct group_info init_groups;
*/
# define CAP_INIT_BSET CAP_FULL_SET
#ifdef CONFIG_RCU_BOOST
#define INIT_TASK_RCU_BOOST() \
.rcu_boost_mutex = NULL,
#else
#define INIT_TASK_RCU_BOOST()
#endif
#ifdef CONFIG_TREE_PREEMPT_RCU
#define INIT_TASK_RCU_TREE_PREEMPT() \
.rcu_blocked_node = NULL,
@ -92,7 +98,8 @@ extern struct group_info init_groups;
.rcu_read_lock_nesting = 0, \
.rcu_read_unlock_special = 0, \
.rcu_node_entry = LIST_HEAD_INIT(tsk.rcu_node_entry), \
INIT_TASK_RCU_TREE_PREEMPT()
INIT_TASK_RCU_TREE_PREEMPT() \
INIT_TASK_RCU_BOOST()
#else
#define INIT_TASK_RCU_PREEMPT(tsk)
#endif

11
include/linux/sched.h
View File

@ -1210,6 +1210,9 @@ struct task_struct {
#ifdef CONFIG_TREE_PREEMPT_RCU
struct rcu_node *rcu_blocked_node;
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
#ifdef CONFIG_RCU_BOOST
struct rt_mutex *rcu_boost_mutex;
#endif /* #ifdef CONFIG_RCU_BOOST */
#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
struct sched_info sched_info;
@ -1745,7 +1748,8 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *
#ifdef CONFIG_PREEMPT_RCU
#define RCU_READ_UNLOCK_BLOCKED (1 << 0) /* blocked while in RCU read-side. */
#define RCU_READ_UNLOCK_NEED_QS (1 << 1) /* RCU core needs CPU response. */
#define RCU_READ_UNLOCK_BOOSTED (1 << 1) /* boosted while in RCU read-side. */
#define RCU_READ_UNLOCK_NEED_QS (1 << 2) /* RCU core needs CPU response. */
static inline void rcu_copy_process(struct task_struct *p)
{
@ -1753,7 +1757,10 @@ static inline void rcu_copy_process(struct task_struct *p)
p->rcu_read_unlock_special = 0;
#ifdef CONFIG_TREE_PREEMPT_RCU
p->rcu_blocked_node = NULL;
#endif
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
#ifdef CONFIG_RCU_BOOST
p->rcu_boost_mutex = NULL;
#endif /* #ifdef CONFIG_RCU_BOOST */
INIT_LIST_HEAD(&p->rcu_node_entry);
}

39
init/Kconfig
View File

@ -450,6 +450,45 @@ config TREE_RCU_TRACE
TREE_PREEMPT_RCU implementations, permitting Makefile to
trivially select kernel/rcutree_trace.c.
config RCU_BOOST
bool "Enable RCU priority boosting"
depends on RT_MUTEXES && TINY_PREEMPT_RCU
default n
help
This option boosts the priority of preempted RCU readers that
block the current preemptible RCU grace period for too long.
This option also prevents heavy loads from blocking RCU
callback invocation for all flavors of RCU.
Say Y here if you are working with real-time apps or heavy loads
Say N here if you are unsure.
config RCU_BOOST_PRIO
int "Real-time priority to boost RCU readers to"
range 1 99
depends on RCU_BOOST
default 1
help
This option specifies the real-time priority to which preempted
RCU readers are to be boosted. If you are working with CPU-bound
real-time applications, you should specify a priority higher then
the highest-priority CPU-bound application.
Specify the real-time priority, or take the default if unsure.
config RCU_BOOST_DELAY
int "Milliseconds to delay boosting after RCU grace-period start"
range 0 3000
depends on RCU_BOOST
default 500
help
This option specifies the time to wait after the beginning of
a given grace period before priority-boosting preempted RCU
readers blocking that grace period. Note that any RCU reader
blocking an expedited RCU grace period is boosted immediately.
Accept the default if unsure.
endmenu # "RCU Subsystem"
config IKCONFIG

66
kernel/rcutiny.c
View File

@ -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);

208
kernel/rcutiny_plugin.h
View File

@ -24,6 +24,29 @@
#include <linux/kthread.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 */
#ifdef CONFIG_TINY_PREEMPT_RCU
#include <linux/delay.h>
@ -48,17 +71,27 @@ struct rcu_preempt_ctrlblk {
struct list_head *gp_tasks;
/* Pointer to the first task blocking the */
/* current grace period, or NULL if there */
/* is not such task. */
/* is no such task. */
struct list_head *exp_tasks;
/* Pointer to first task blocking the */
/* current expedited grace period, or NULL */
/* if there is no such task. If there */
/* is no current expedited grace period, */
/* then there cannot be any such task. */
#ifdef CONFIG_RCU_BOOST
struct list_head *boost_tasks;
/* Pointer to first task that needs to be */
/* priority-boosted, or NULL if no priority */
/* boosting is needed. If there is no */
/* current or expedited grace period, there */
/* can be no such task. */
#endif /* #ifdef CONFIG_RCU_BOOST */
u8 gpnum; /* Current grace period. */
u8 gpcpu; /* Last grace period blocked by the CPU. */
u8 completed; /* Last grace period completed. */
/* If all three are equal, RCU is idle. */
s8 boosted_this_gp; /* Has boosting already happened? */
unsigned long boost_time; /* When to start boosting (jiffies) */
};
static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = {
@ -123,6 +156,130 @@ static int rcu_preempt_gp_in_progress(void)
return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum;
}
/*
* Advance a ->blkd_tasks-list pointer to the next entry, instead
* returning NULL if at the end of the list.
*/
static struct list_head *rcu_next_node_entry(struct task_struct *t)
{
struct list_head *np;
np = t->rcu_node_entry.next;
if (np == &rcu_preempt_ctrlblk.blkd_tasks)
np = NULL;
return np;
}
#ifdef CONFIG_RCU_BOOST
#include "rtmutex_common.h"
/*
* 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.
*/
static int rcu_boost(void)
{
unsigned long flags;
struct rt_mutex mtx;
struct list_head *np;
struct task_struct *t;
if (rcu_preempt_ctrlblk.boost_tasks == NULL)
return 0; /* Nothing to boost. */
raw_local_irq_save(flags);
rcu_preempt_ctrlblk.boosted_this_gp++;
t = container_of(rcu_preempt_ctrlblk.boost_tasks, struct task_struct,
rcu_node_entry);
np = rcu_next_node_entry(t);
rt_mutex_init_proxy_locked(&mtx, t);
t->rcu_boost_mutex = &mtx;
t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED;
raw_local_irq_restore(flags);
rt_mutex_lock(&mtx);
rt_mutex_unlock(&mtx);
return rcu_preempt_ctrlblk.boost_tasks != NULL;
}
/*
* Check to see if it is now time to start boosting RCU readers blocking
* the current grace period, and, if so, tell the rcu_kthread_task to
* start boosting them. If there is an expedited boost in progress,
* we wait for it to complete.
*/
static void rcu_initiate_boost(void)
{
if (rcu_preempt_ctrlblk.gp_tasks != NULL &&
rcu_preempt_ctrlblk.boost_tasks == NULL &&
rcu_preempt_ctrlblk.boosted_this_gp == 0 &&
ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time)) {
rcu_preempt_ctrlblk.boost_tasks = rcu_preempt_ctrlblk.gp_tasks;
invoke_rcu_kthread();
}
}
/*
* Initiate boosting for an expedited grace period.
*/
static void rcu_initiate_expedited_boost(void)
{
unsigned long flags;
raw_local_irq_save(flags);
if (!list_empty(&rcu_preempt_ctrlblk.blkd_tasks)) {
rcu_preempt_ctrlblk.boost_tasks =
rcu_preempt_ctrlblk.blkd_tasks.next;
rcu_preempt_ctrlblk.boosted_this_gp = -1;
invoke_rcu_kthread();
}
raw_local_irq_restore(flags);
}
#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000);
/*
* Do priority-boost accounting for the start of a new grace period.
*/
static void rcu_preempt_boost_start_gp(void)
{
rcu_preempt_ctrlblk.boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
if (rcu_preempt_ctrlblk.boosted_this_gp > 0)
rcu_preempt_ctrlblk.boosted_this_gp = 0;
}
#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.
*/
static void rcu_initiate_boost(void)
{
}
/*
* If there is no RCU priority boosting, we don't initiate expedited boosting.
*/
static void rcu_initiate_expedited_boost(void)
{
}
/*
* If there is no RCU priority boosting, nothing to do at grace-period start.
*/
static void rcu_preempt_boost_start_gp(void)
{
}
#endif /* else #ifdef CONFIG_RCU_BOOST */
/*
* Record a preemptible-RCU quiescent state for the specified CPU. Note
* that this just means that the task currently running on the CPU is
@ -150,12 +307,14 @@ static void rcu_preempt_cpu_qs(void)
rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum;
current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
/*
* If there is no GP, or if blocked readers are still blocking GP,
* then there is nothing more to do.
*/
/* If there is no GP then there is nothing more to do. */
if (!rcu_preempt_gp_in_progress() || rcu_preempt_blocked_readers_cgp())
return;
/* If there are blocked readers, go check up on boosting. */
if (rcu_preempt_blocked_readers_cgp()) {
rcu_initiate_boost();
return;
}
/* Advance callbacks. */
rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum;
@ -168,7 +327,7 @@ 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_cbs();
invoke_rcu_kthread();
}
/*
@ -186,6 +345,9 @@ static void rcu_preempt_start_gp(void)
rcu_preempt_ctrlblk.gp_tasks =
rcu_preempt_ctrlblk.blkd_tasks.next;
/* Set up for RCU priority boosting. */
rcu_preempt_boost_start_gp();
/* If there is no running reader, CPU is done with GP. */
if (!rcu_preempt_running_reader())
rcu_preempt_cpu_qs();
@ -306,14 +468,16 @@ static void rcu_read_unlock_special(struct task_struct *t)
*/
empty = !rcu_preempt_blocked_readers_cgp();
empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL;
np = t->rcu_node_entry.next;
if (np == &rcu_preempt_ctrlblk.blkd_tasks)
np = NULL;
np = rcu_next_node_entry(t);
list_del(&t->rcu_node_entry);
if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks)
rcu_preempt_ctrlblk.gp_tasks = np;
if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks)
rcu_preempt_ctrlblk.exp_tasks = np;
#ifdef CONFIG_RCU_BOOST
if (&t->rcu_node_entry == rcu_preempt_ctrlblk.boost_tasks)
rcu_preempt_ctrlblk.boost_tasks = np;
#endif /* #ifdef CONFIG_RCU_BOOST */
INIT_LIST_HEAD(&t->rcu_node_entry);
/*
@ -333,6 +497,14 @@ static void rcu_read_unlock_special(struct task_struct *t)
if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL)
rcu_report_exp_done();
}
#ifdef CONFIG_RCU_BOOST
/* Unboost self if was boosted. */
if (special & RCU_READ_UNLOCK_BOOSTED) {
t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED;
rt_mutex_unlock(t->rcu_boost_mutex);
t->rcu_boost_mutex = NULL;
}
#endif /* #ifdef CONFIG_RCU_BOOST */
local_irq_restore(flags);
}
@ -376,7 +548,7 @@ static void rcu_preempt_check_callbacks(void)
rcu_preempt_cpu_qs();
if (&rcu_preempt_ctrlblk.rcb.rcucblist !=
rcu_preempt_ctrlblk.rcb.donetail)
invoke_rcu_cbs();
invoke_rcu_kthread();
if (rcu_preempt_gp_in_progress() &&
rcu_cpu_blocking_cur_gp() &&
rcu_preempt_running_reader())
@ -534,6 +706,7 @@ void synchronize_rcu_expedited(void)
/* Wait for tail of ->blkd_tasks list to drain. */
if (rcu_preempted_readers_exp())
rcu_initiate_expedited_boost();
wait_event(sync_rcu_preempt_exp_wq,
!rcu_preempted_readers_exp());
@ -574,6 +747,15 @@ void exit_rcu(void)
#else /* #ifdef CONFIG_TINY_PREEMPT_RCU */
/*
* 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.
@ -614,3 +796,9 @@ 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 */