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Commit a46e0899 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: use softirq instead of kthreads except when RCU_BOOST=y 



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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 09223371

kernel/rcutree.c

+44 −15
Original line number Diff line number Diff line
@@ -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.

 */

kernel/rcutree.h

+6 −2
Original line number Diff line number Diff line
@@ -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 */

kernel/rcutree_plugin.h

+26 −15
Original line number Diff line number Diff line
@@ -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;

}

kernel/rcutree_trace.c

+23 −9
Original line number Diff line number Diff line
@@ -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);