Commit cafafd67 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu-tasks: Create per-CPU callback lists 



Currently, RCU Tasks Trace (as well as the other two flavors of RCU Tasks)
use a single global callback list.  This works well and is simple, but
expected changes in workload will cause this list to become a bottleneck.
This commit therefore creates per-CPU callback lists for the various
flavors of RCU Tasks, but continues queueing on a single list, namely
that of CPU 0.  Later commits will dynamically vary the number of lists
in use to accommodate dynamic changes in workload.

Reported-by: default avatarMartin Lau <kafai@fb.com>
Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Tested-by: default avatarkernel test robot <beibei.si@intel.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent f5dbc594

kernel/rcu/tasks.h

+78 −28
Original line number Diff line number Diff line
@@ -20,11 +20,21 @@ typedef void (*holdouts_func_t)(struct list_head *hop, bool ndrpt, bool *frptp); 
typedef void (*postgp_func_t)(struct rcu_tasks *rtp);



/**

 * struct rcu_tasks - Definition for a Tasks-RCU-like mechanism.

 * struct rcu_tasks_percpu - Per-CPU component of definition for a Tasks-RCU-like mechanism.

 * @cbs_head: Head of callback list.

 * @cbs_tail: Tail pointer for callback list.

 * @cbs_pcpu_lock: Lock protecting per-CPU callback list.

 */

struct rcu_tasks_percpu {

	struct rcu_head *cbs_head;

	struct rcu_head **cbs_tail;

	raw_spinlock_t cbs_pcpu_lock;

};



/**

 * struct rcu_tasks - Definition for a Tasks-RCU-like mechanism.

 * @cbs_wq: Wait queue allowing new callback to get kthread's attention.

 * @cbs_lock: Lock protecting callback list.

 * @cbs_gbl_lock: Lock protecting callback list.

 * @kthread_ptr: This flavor's grace-period/callback-invocation kthread.

 * @gp_func: This flavor's grace-period-wait function.

 * @gp_state: Grace period's most recent state transition (debugging).
@@ -41,14 +51,13 @@ typedef void (*postgp_func_t)(struct rcu_tasks *rtp); 
 * @holdouts_func: This flavor's holdout-list scan function (optional).

 * @postgp_func: This flavor's post-grace-period function (optional).

 * @call_func: This flavor's call_rcu()-equivalent function.

 * @rtpcpu: This flavor's rcu_tasks_percpu structure.

 * @name: This flavor's textual name.

 * @kname: This flavor's kthread name.

 */

struct rcu_tasks {

	struct rcu_head *cbs_head;

	struct rcu_head **cbs_tail;

	struct wait_queue_head cbs_wq;

	raw_spinlock_t cbs_lock;

	raw_spinlock_t cbs_gbl_lock;

	int gp_state;

	int gp_sleep;

	int init_fract;
@@ -65,18 +74,22 @@ struct rcu_tasks { 
	holdouts_func_t holdouts_func;

	postgp_func_t postgp_func;

	call_rcu_func_t call_func;

	struct rcu_tasks_percpu __percpu *rtpcpu;

	char *name;

	char *kname;

};



#define DEFINE_RCU_TASKS(rt_name, gp, call, n)						\

static DEFINE_PER_CPU(struct rcu_tasks_percpu, rt_name ## __percpu) = {			\

	.cbs_pcpu_lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name ## __percpu.cbs_pcpu_lock),	\

};											\

static struct rcu_tasks rt_name =							\

{											\

	.cbs_tail = &rt_name.cbs_head,					\

	.cbs_wq = __WAIT_QUEUE_HEAD_INITIALIZER(rt_name.cbs_wq),			\

	.cbs_lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name.cbs_lock),		\

	.cbs_gbl_lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name.cbs_gbl_lock),			\

	.gp_func = gp,									\

	.call_func = call,								\

	.rtpcpu = &rt_name ## __percpu,							\

	.name = n,									\

	.kname = #rt_name,								\

}
@@ -148,20 +161,51 @@ static const char *tasks_gp_state_getname(struct rcu_tasks *rtp) 
}

#endif /* #ifndef CONFIG_TINY_RCU */



// Initialize per-CPU callback lists for the specified flavor of

// Tasks RCU.

static void cblist_init_generic(struct rcu_tasks *rtp)

{

	int cpu;

	unsigned long flags;



	raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags);

	for_each_possible_cpu(cpu) {

		struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);



		WARN_ON_ONCE(!rtpcp);

		if (cpu)

			raw_spin_lock_init(&rtpcp->cbs_pcpu_lock);

		raw_spin_lock(&rtpcp->cbs_pcpu_lock); // irqs already disabled.

		if (!WARN_ON_ONCE(rtpcp->cbs_tail))

			rtpcp->cbs_tail = &rtpcp->cbs_head;

		raw_spin_unlock(&rtpcp->cbs_pcpu_lock); // irqs remain disabled.

	}

	raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);



}



// Enqueue a callback for the specified flavor of Tasks RCU.

static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,

				   struct rcu_tasks *rtp)

{

	unsigned long flags;

	bool needwake;

	struct rcu_tasks_percpu *rtpcp;



	rhp->next = NULL;

	rhp->func = func;

	raw_spin_lock_irqsave(&rtp->cbs_lock, flags);

	needwake = !rtp->cbs_head;

	WRITE_ONCE(*rtp->cbs_tail, rhp);

	rtp->cbs_tail = &rhp->next;

	raw_spin_unlock_irqrestore(&rtp->cbs_lock, flags);

	local_irq_save(flags);

	rtpcp = per_cpu_ptr(rtp->rtpcpu, 0 /* smp_processor_id() */);

	raw_spin_lock(&rtpcp->cbs_pcpu_lock);

	if (!rtpcp->cbs_tail) {

		raw_spin_unlock(&rtpcp->cbs_pcpu_lock); // irqs remain disabled.

		cblist_init_generic(rtp);

		raw_spin_lock(&rtpcp->cbs_pcpu_lock); // irqs already disabled.

	}

	needwake = !rtpcp->cbs_head;

	WRITE_ONCE(*rtpcp->cbs_tail, rhp);

	rtpcp->cbs_tail = &rhp->next;

	raw_spin_unlock_irqrestore(&rtpcp->cbs_pcpu_lock, flags);

	/* We can't create the thread unless interrupts are enabled. */

	if (needwake && READ_ONCE(rtp->kthread_ptr))

		wake_up(&rtp->cbs_wq);
@@ -197,21 +241,23 @@ static int __noreturn rcu_tasks_kthread(void *arg) 
	 * This loop is terminated by the system going down.  ;-)

	 */

	for (;;) {

		struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, 0);  // for_each...



		set_tasks_gp_state(rtp, RTGS_WAIT_CBS);



		/* Pick up any new callbacks. */

		raw_spin_lock_irqsave(&rtp->cbs_lock, flags);

		raw_spin_lock_irqsave(&rtpcp->cbs_pcpu_lock, flags);

		smp_mb__after_spinlock(); // Order updates vs. GP.

		list = rtp->cbs_head;

		rtp->cbs_head = NULL;

		rtp->cbs_tail = &rtp->cbs_head;

		raw_spin_unlock_irqrestore(&rtp->cbs_lock, flags);

		list = rtpcp->cbs_head;

		rtpcp->cbs_head = NULL;

		rtpcp->cbs_tail = &rtpcp->cbs_head;

		raw_spin_unlock_irqrestore(&rtpcp->cbs_pcpu_lock, flags);



		/* If there were none, wait a bit and start over. */

		if (!list) {

			wait_event_interruptible(rtp->cbs_wq,

						 READ_ONCE(rtp->cbs_head));

			if (!rtp->cbs_head) {

						 READ_ONCE(rtpcp->cbs_head));

			if (!rtpcp->cbs_head) {

				WARN_ON(signal_pending(current));

				set_tasks_gp_state(rtp, RTGS_WAIT_WAIT_CBS);

				schedule_timeout_idle(HZ/10);
@@ -279,6 +325,7 @@ static void __init rcu_tasks_bootup_oddness(void) 
/* Dump out rcutorture-relevant state common to all RCU-tasks flavors. */

static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)

{

	struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, 0); // for_each...

	pr_info("%s: %s(%d) since %lu g:%lu i:%lu/%lu %c%c %s\n",

		rtp->kname,

		tasks_gp_state_getname(rtp), data_race(rtp->gp_state),
@@ -286,7 +333,7 @@ static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s) 
		data_race(rtp->n_gps),

		data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis),

		".k"[!!data_race(rtp->kthread_ptr)],

		".C"[!!data_race(rtp->cbs_head)],

		".C"[!!data_race(rtpcp->cbs_head)],

		s);

}

#endif // #ifndef CONFIG_TINY_RCU
@@ -593,6 +640,7 @@ EXPORT_SYMBOL_GPL(rcu_barrier_tasks); 


static int __init rcu_spawn_tasks_kthread(void)

{

	cblist_init_generic(&rcu_tasks);

	rcu_tasks.gp_sleep = HZ / 10;

	rcu_tasks.init_fract = HZ / 10;

	rcu_tasks.pregp_func = rcu_tasks_pregp_step;
@@ -731,6 +779,7 @@ EXPORT_SYMBOL_GPL(rcu_barrier_tasks_rude); 


static int __init rcu_spawn_tasks_rude_kthread(void)

{

	cblist_init_generic(&rcu_tasks_rude);

	rcu_tasks_rude.gp_sleep = HZ / 10;

	rcu_spawn_tasks_kthread_generic(&rcu_tasks_rude);

	return 0;
@@ -1264,6 +1313,7 @@ EXPORT_SYMBOL_GPL(rcu_barrier_tasks_trace); 


static int __init rcu_spawn_tasks_trace_kthread(void)

{

	cblist_init_generic(&rcu_tasks_trace);

	if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) {

		rcu_tasks_trace.gp_sleep = HZ / 10;

		rcu_tasks_trace.init_fract = HZ / 10;