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Commit 0446be48 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Paul E. McKenney
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rcu: Abstract rcu_start_future_gp() from rcu_nocb_wait_gp() 



CPUs going idle will need to record the need for a future grace
period, but won't actually need to block waiting on it.  This commit
therefore splits rcu_start_future_gp(), which does the recording, from
rcu_nocb_wait_gp(), which now invokes rcu_start_future_gp() to do the
recording, after which rcu_nocb_wait_gp() does the waiting.

Signed-off-by: default avatarPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 8b425aa8

kernel/rcutree.c

+119 −4
Original line number Diff line number Diff line
@@ -224,6 +224,7 @@ static ulong jiffies_till_next_fqs = RCU_JIFFIES_TILL_FORCE_QS; 
module_param(jiffies_till_first_fqs, ulong, 0644);

module_param(jiffies_till_next_fqs, ulong, 0644);



static void rcu_start_gp(struct rcu_state *rsp);

static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *));

static void force_quiescent_state(struct rcu_state *rsp);

static int rcu_pending(int cpu);
@@ -1074,6 +1075,120 @@ static unsigned long rcu_cbs_completed(struct rcu_state *rsp, 
	return rnp->completed + 2;

}



/*

 * Trace-event helper function for rcu_start_future_gp() and

 * rcu_nocb_wait_gp().

 */

static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,

				unsigned long c, char *s)

{

	trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,

				      rnp->completed, c, rnp->level,

				      rnp->grplo, rnp->grphi, s);

}



/*

 * Start some future grace period, as needed to handle newly arrived

 * callbacks.  The required future grace periods are recorded in each

 * rcu_node structure's ->need_future_gp field.

 *

 * The caller must hold the specified rcu_node structure's ->lock.

 */

static unsigned long __maybe_unused

rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp)

{

	unsigned long c;

	int i;

	struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);



	/*

	 * Pick up grace-period number for new callbacks.  If this

	 * grace period is already marked as needed, return to the caller.

	 */

	c = rcu_cbs_completed(rdp->rsp, rnp);

	trace_rcu_future_gp(rnp, rdp, c, "Startleaf");

	if (rnp->need_future_gp[c & 0x1]) {

		trace_rcu_future_gp(rnp, rdp, c, "Prestartleaf");

		return c;

	}



	/*

	 * If either this rcu_node structure or the root rcu_node structure

	 * believe that a grace period is in progress, then we must wait

	 * for the one following, which is in "c".  Because our request

	 * will be noticed at the end of the current grace period, we don't

	 * need to explicitly start one.

	 */

	if (rnp->gpnum != rnp->completed ||

	    ACCESS_ONCE(rnp->gpnum) != ACCESS_ONCE(rnp->completed)) {

		rnp->need_future_gp[c & 0x1]++;

		trace_rcu_future_gp(rnp, rdp, c, "Startedleaf");

		return c;

	}



	/*

	 * There might be no grace period in progress.  If we don't already

	 * hold it, acquire the root rcu_node structure's lock in order to

	 * start one (if needed).

	 */

	if (rnp != rnp_root)

		raw_spin_lock(&rnp_root->lock);



	/*

	 * Get a new grace-period number.  If there really is no grace

	 * period in progress, it will be smaller than the one we obtained

	 * earlier.  Adjust callbacks as needed.  Note that even no-CBs

	 * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.

	 */

	c = rcu_cbs_completed(rdp->rsp, rnp_root);

	for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++)

		if (ULONG_CMP_LT(c, rdp->nxtcompleted[i]))

			rdp->nxtcompleted[i] = c;



	/*

	 * If the needed for the required grace period is already

	 * recorded, trace and leave.

	 */

	if (rnp_root->need_future_gp[c & 0x1]) {

		trace_rcu_future_gp(rnp, rdp, c, "Prestartedroot");

		goto unlock_out;

	}



	/* Record the need for the future grace period. */

	rnp_root->need_future_gp[c & 0x1]++;



	/* If a grace period is not already in progress, start one. */

	if (rnp_root->gpnum != rnp_root->completed) {

		trace_rcu_future_gp(rnp, rdp, c, "Startedleafroot");

	} else {

		trace_rcu_future_gp(rnp, rdp, c, "Startedroot");

		rcu_start_gp(rdp->rsp);

	}

unlock_out:

	if (rnp != rnp_root)

		raw_spin_unlock(&rnp_root->lock);

	return c;

}



/*

 * Clean up any old requests for the just-ended grace period.  Also return

 * whether any additional grace periods have been requested.  Also invoke

 * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads

 * waiting for this grace period to complete.

 */

static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)

{

	int c = rnp->completed;

	int needmore;

	struct rcu_data *rdp = this_cpu_ptr(rsp->rda);



	rcu_nocb_gp_cleanup(rsp, rnp);

	rnp->need_future_gp[c & 0x1] = 0;

	needmore = rnp->need_future_gp[(c + 1) & 0x1];

	trace_rcu_future_gp(rnp, rdp, c, needmore ? "CleanupMore" : "Cleanup");

	return needmore;

}



/*

 * If there is room, assign a ->completed number to any callbacks on

 * this CPU that have not already been assigned.  Also accelerate any
@@ -1312,9 +1427,9 @@ static int rcu_gp_init(struct rcu_state *rsp) 
		rdp = this_cpu_ptr(rsp->rda);

		rcu_preempt_check_blocked_tasks(rnp);

		rnp->qsmask = rnp->qsmaskinit;

		rnp->gpnum = rsp->gpnum;

		ACCESS_ONCE(rnp->gpnum) = rsp->gpnum;

		WARN_ON_ONCE(rnp->completed != rsp->completed);

		rnp->completed = rsp->completed;

		ACCESS_ONCE(rnp->completed) = rsp->completed;

		if (rnp == rdp->mynode)

			rcu_start_gp_per_cpu(rsp, rnp, rdp);

		rcu_preempt_boost_start_gp(rnp);
@@ -1395,11 +1510,11 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) 
	 */

	rcu_for_each_node_breadth_first(rsp, rnp) {

		raw_spin_lock_irq(&rnp->lock);

		rnp->completed = rsp->gpnum;

		ACCESS_ONCE(rnp->completed) = rsp->gpnum;

		rdp = this_cpu_ptr(rsp->rda);

		if (rnp == rdp->mynode)

			__rcu_process_gp_end(rsp, rnp, rdp);

		nocb += rcu_nocb_gp_cleanup(rsp, rnp);

		nocb += rcu_future_gp_cleanup(rsp, rnp);

		raw_spin_unlock_irq(&rnp->lock);

		cond_resched();

	}

kernel/rcutree.h

+1 −1
Original line number Diff line number Diff line
@@ -526,7 +526,7 @@ static void zero_cpu_stall_ticks(struct rcu_data *rdp); 
static void increment_cpu_stall_ticks(void);

static int rcu_nocb_needs_gp(struct rcu_state *rsp);

static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq);

static int rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp);

static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp);

static void rcu_init_one_nocb(struct rcu_node *rnp);

static bool is_nocb_cpu(int cpu);

static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,

kernel/rcutree_plugin.h

+10 −94
Original line number Diff line number Diff line
@@ -2022,22 +2022,12 @@ static int rcu_nocb_needs_gp(struct rcu_state *rsp) 
}



/*

 * Clean up this rcu_node structure's no-CBs state at the end of

 * a grace period, and also return whether any no-CBs CPU associated

 * with this rcu_node structure needs another grace period.

 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended

 * grace period.

 */

static int rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)

static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)

{

	int c = rnp->completed;

	int needmore;



	wake_up_all(&rnp->nocb_gp_wq[c & 0x1]);

	rnp->need_future_gp[c & 0x1] = 0;

	needmore = rnp->need_future_gp[(c + 1) & 0x1];

	trace_rcu_future_grace_period(rsp->name, rnp->gpnum, rnp->completed,

				      c, rnp->level, rnp->grplo, rnp->grphi,

				      needmore ? "CleanupMore" : "Cleanup");

	return needmore;

	wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);

}



/*
@@ -2175,84 +2165,16 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp) 
	bool d;

	unsigned long flags;

	struct rcu_node *rnp = rdp->mynode;

	struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);



	raw_spin_lock_irqsave(&rnp->lock, flags);

	c = rnp->completed + 2;



	/* Count our request for a grace period. */

	rnp->need_future_gp[c & 0x1]++;

	trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,

				      rnp->completed, c, rnp->level,

				      rnp->grplo, rnp->grphi, "Startleaf");



	if (rnp->gpnum != rnp->completed) {



		/*

		 * This rcu_node structure believes that a grace period

		 * is in progress, so we are done.  When this grace

		 * period ends, our request will be acted upon.

		 */

		trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,

					      rnp->completed, c, rnp->level,

					      rnp->grplo, rnp->grphi,

					      "Startedleaf");

		raw_spin_unlock_irqrestore(&rnp->lock, flags);



	} else {



		/*

		 * Might not be a grace period, check root rcu_node

		 * structure to see if we must start one.

		 */

		if (rnp != rnp_root)

			raw_spin_lock(&rnp_root->lock); /* irqs disabled. */

		if (rnp_root->gpnum != rnp_root->completed) {

			trace_rcu_future_grace_period(rdp->rsp->name,

						      rnp->gpnum,

						      rnp->completed,

						      c, rnp->level,

						      rnp->grplo, rnp->grphi,

						      "Startedleafroot");

			raw_spin_unlock(&rnp_root->lock); /* irqs disabled. */

		} else {



			/*

			 * No grace period, so we need to start one.

			 * The good news is that we can wait for exactly

			 * one grace period instead of part of the current

			 * grace period and all of the next grace period.

			 * Adjust counters accordingly and start the

			 * needed grace period.

			 */

			rnp->need_future_gp[c & 0x1]--;

			c = rnp_root->completed + 1;

			rnp->need_future_gp[c & 0x1]++;

			rnp_root->need_future_gp[c & 0x1]++;

			trace_rcu_future_grace_period(rdp->rsp->name,

						      rnp->gpnum,

						      rnp->completed,

						      c, rnp->level,

						      rnp->grplo, rnp->grphi,

						      "Startedroot");

			rcu_start_gp(rdp->rsp);

			raw_spin_unlock(&rnp->lock);

		}



		/* Clean up locking and irq state. */

		if (rnp != rnp_root)

	c = rcu_start_future_gp(rnp, rdp);

	raw_spin_unlock_irqrestore(&rnp->lock, flags);

		else

			local_irq_restore(flags);

	}



	/*

	 * Wait for the grace period.  Do so interruptibly to avoid messing

	 * up the load average.

	 */

	trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,

				      rnp->completed, c, rnp->level,

				      rnp->grplo, rnp->grphi, "StartWait");

	trace_rcu_future_gp(rnp, rdp, c, "StartWait");

	for (;;) {

		wait_event_interruptible(

			rnp->nocb_gp_wq[c & 0x1],
@@ -2260,14 +2182,9 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp) 
		if (likely(d))

			break;

		flush_signals(current);

		trace_rcu_future_grace_period(rdp->rsp->name,

					      rnp->gpnum, rnp->completed, c,

					      rnp->level, rnp->grplo,

					      rnp->grphi, "ResumeWait");

	}

	trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,

				      rnp->completed, c, rnp->level,

				      rnp->grplo, rnp->grphi, "EndWait");

		trace_rcu_future_gp(rnp, rdp, c, "ResumeWait");

	}

	trace_rcu_future_gp(rnp, rdp, c, "EndWait");

	smp_mb(); /* Ensure that CB invocation happens after GP end. */

}
@@ -2375,9 +2292,8 @@ static int rcu_nocb_needs_gp(struct rcu_state *rsp) 
	return 0;

}



static int rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)

static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)

{

	return 0;

}



static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)