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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
View File

@ -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.
*/

8
kernel/rcutree.h
View File

@ -369,6 +369,7 @@ struct rcu_state {
/* period because */
/* force_quiescent_state() */
/* was running. */
u8 boost; /* Subject to priority boost. */
unsigned long gpnum; /* Current gp number. */
unsigned long completed; /* # of last completed gp. */
@ -439,7 +440,6 @@ static void rcu_preempt_offline_cpu(int cpu);
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
static void rcu_preempt_check_callbacks(int cpu);
static void rcu_preempt_process_callbacks(void);
static void rcu_preempt_do_callbacks(void);
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU)
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp);
@ -451,11 +451,15 @@ static void rcu_preempt_send_cbs_to_online(void);
static void __init __rcu_init_preempt(void);
static void rcu_needs_cpu_flush(void);
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
static void invoke_rcu_callbacks_kthread(void);
#ifdef CONFIG_RCU_BOOST
static void rcu_preempt_do_callbacks(void);
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
cpumask_var_t cm);
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
struct rcu_node *rnp,
int rnp_index);
#endif /* #ifdef CONFIG_RCU_BOOST */
#endif /* #ifndef RCU_TREE_NONCORE */

41
kernel/rcutree_plugin.h
View File

@ -602,11 +602,15 @@ static void rcu_preempt_process_callbacks(void)
&__get_cpu_var(rcu_preempt_data));
}
#ifdef CONFIG_RCU_BOOST
static void rcu_preempt_do_callbacks(void)
{
rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data));
}
#endif /* #ifdef CONFIG_RCU_BOOST */
/*
* Queue a preemptible-RCU callback for invocation after a grace period.
*/
@ -1002,10 +1006,6 @@ static void rcu_preempt_process_callbacks(void)
{
}
static void rcu_preempt_do_callbacks(void)
{
}
/*
* Wait for an rcu-preempt grace period, but make it happen quickly.
* But because preemptible RCU does not exist, map to rcu-sched.
@ -1257,6 +1257,23 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
}
}
/*
* Wake up the per-CPU kthread to invoke RCU callbacks.
*/
static void invoke_rcu_callbacks_kthread(void)
{
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);
return;
}
wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
local_irq_restore(flags);
}
/*
* Set the affinity of the boost kthread. The CPU-hotplug locks are
* held, so no one should be messing with the existence of the boost
@ -1297,6 +1314,7 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
if (&rcu_preempt_state != rsp)
return 0;
rsp->boost = 1;
if (rnp->boost_kthread_task != NULL)
return 0;
t = kthread_create(rcu_boost_kthread, (void *)rnp,
@ -1319,22 +1337,15 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
cpumask_var_t cm)
static void invoke_rcu_callbacks_kthread(void)
{
WARN_ON_ONCE(1);
}
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
}
static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
struct rcu_node *rnp,
int rnp_index)
{
return 0;
}
#endif /* #else #ifdef CONFIG_RCU_BOOST */
#ifndef CONFIG_SMP
@ -1509,7 +1520,7 @@ static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);
*
* Because it is not legal to invoke rcu_process_callbacks() with irqs
* disabled, we do one pass of force_quiescent_state(), then do a
* invoke_rcu_cpu_kthread() to cause rcu_process_callbacks() to be invoked
* invoke_rcu_core() to cause rcu_process_callbacks() to be invoked
* later. The per-cpu rcu_dyntick_drain variable controls the sequencing.
*/
int rcu_needs_cpu(int cpu)
@ -1560,7 +1571,7 @@ int rcu_needs_cpu(int cpu)
/* If RCU callbacks are still pending, RCU still needs this CPU. */
if (c)
invoke_rcu_cpu_kthread();
invoke_rcu_core();
return c;
}

32
kernel/rcutree_trace.c
View File

@ -46,6 +46,8 @@
#define RCU_TREE_NONCORE
#include "rcutree.h"
#ifdef CONFIG_RCU_BOOST
DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_cpu);
DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
@ -58,6 +60,8 @@ static char convert_kthread_status(unsigned int kthread_status)
return "SRWOY"[kthread_status];
}
#endif /* #ifdef CONFIG_RCU_BOOST */
static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
{
if (!rdp->beenonline)
@ -76,7 +80,7 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
rdp->dynticks_fqs);
#endif /* #ifdef CONFIG_NO_HZ */
seq_printf(m, " of=%lu ri=%lu", rdp->offline_fqs, rdp->resched_ipi);
seq_printf(m, " ql=%ld qs=%c%c%c%c kt=%d/%c/%d ktl=%x b=%ld",
seq_printf(m, " ql=%ld qs=%c%c%c%c",
rdp->qlen,
".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
rdp->nxttail[RCU_NEXT_TAIL]],
@ -84,13 +88,16 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
rdp->nxttail[RCU_NEXT_READY_TAIL]],
".W"[rdp->nxttail[RCU_DONE_TAIL] !=
rdp->nxttail[RCU_WAIT_TAIL]],
".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]],
".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]]);
#ifdef CONFIG_RCU_BOOST
seq_printf(m, " kt=%d/%c/%d ktl=%x",
per_cpu(rcu_cpu_has_work, rdp->cpu),
convert_kthread_status(per_cpu(rcu_cpu_kthread_status,
rdp->cpu)),
per_cpu(rcu_cpu_kthread_cpu, rdp->cpu),
per_cpu(rcu_cpu_kthread_loops, rdp->cpu) & 0xffff,
rdp->blimit);
per_cpu(rcu_cpu_kthread_loops, rdp->cpu) & 0xffff);
#endif /* #ifdef CONFIG_RCU_BOOST */
seq_printf(m, " b=%ld", rdp->blimit);
seq_printf(m, " ci=%lu co=%lu ca=%lu\n",
rdp->n_cbs_invoked, rdp->n_cbs_orphaned, rdp->n_cbs_adopted);
}
@ -147,18 +154,21 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp)
rdp->dynticks_fqs);
#endif /* #ifdef CONFIG_NO_HZ */
seq_printf(m, ",%lu,%lu", rdp->offline_fqs, rdp->resched_ipi);
seq_printf(m, ",%ld,\"%c%c%c%c\",%d,\"%c\",%ld", rdp->qlen,
seq_printf(m, ",%ld,\"%c%c%c%c\"", rdp->qlen,
".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
rdp->nxttail[RCU_NEXT_TAIL]],
".R"[rdp->nxttail[RCU_WAIT_TAIL] !=
rdp->nxttail[RCU_NEXT_READY_TAIL]],
".W"[rdp->nxttail[RCU_DONE_TAIL] !=
rdp->nxttail[RCU_WAIT_TAIL]],
".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]],
".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]]);
#ifdef CONFIG_RCU_BOOST
seq_printf(m, ",%d,\"%c\"",
per_cpu(rcu_cpu_has_work, rdp->cpu),
convert_kthread_status(per_cpu(rcu_cpu_kthread_status,
rdp->cpu)),
rdp->blimit);
rdp->cpu)));
#endif /* #ifdef CONFIG_RCU_BOOST */
seq_printf(m, ",%ld", rdp->blimit);
seq_printf(m, ",%lu,%lu,%lu\n",
rdp->n_cbs_invoked, rdp->n_cbs_orphaned, rdp->n_cbs_adopted);
}
@ -169,7 +179,11 @@ static int show_rcudata_csv(struct seq_file *m, void *unused)
#ifdef CONFIG_NO_HZ
seq_puts(m, "\"dt\",\"dt nesting\",\"dt NMI nesting\",\"df\",");
#endif /* #ifdef CONFIG_NO_HZ */
seq_puts(m, "\"of\",\"ri\",\"ql\",\"b\",\"ci\",\"co\",\"ca\"\n");
seq_puts(m, "\"of\",\"ri\",\"ql\",\"qs\"");
#ifdef CONFIG_RCU_BOOST
seq_puts(m, "\"kt\",\"ktl\"");
#endif /* #ifdef CONFIG_RCU_BOOST */
seq_puts(m, ",\"b\",\"ci\",\"co\",\"ca\"\n");
#ifdef CONFIG_TREE_PREEMPT_RCU
seq_puts(m, "\"rcu_preempt:\"\n");
PRINT_RCU_DATA(rcu_preempt_data, print_one_rcu_data_csv, m);