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Commit c1935209 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Simplify and inline cpu_needs_another_gp() 



Now that RCU no longer relies on failsafe checks, cpu_needs_another_gp()
can be greatly simplified.  This simplification eliminates the last
call to rcu_future_needs_gp() and to rcu_segcblist_future_gp_needed(),
both of which which can then be eliminated.  And then, because
cpu_needs_another_gp() is called only from __rcu_pending(), it can be
inlined and eliminated.

This commit carries out the simplification, inlining, and elimination
called out above.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: default avatarNicholas Piggin <npiggin@gmail.com>
parent 384f77f4

kernel/rcu/rcu_segcblist.c

+0 −18
Original line number Diff line number Diff line
@@ -403,24 +403,6 @@ bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq) 
	return true;

}



/*

 * Scan the specified rcu_segcblist structure for callbacks that need

 * a grace period later than the one specified by "seq".  We don't look

 * at the RCU_DONE_TAIL or RCU_NEXT_TAIL segments because they don't

 * have a grace-period sequence number.

 */

bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,

				    unsigned long seq)

{

	int i;



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

		if (rsclp->tails[i - 1] != rsclp->tails[i] &&

		    ULONG_CMP_LT(seq, rsclp->gp_seq[i]))

			return true;

	return false;

}



/*

 * Merge the source rcu_segcblist structure into the destination

 * rcu_segcblist structure, then initialize the source.  Any pending

kernel/rcu/rcu_segcblist.h

+0 −2
Original line number Diff line number Diff line
@@ -134,7 +134,5 @@ void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp, 
				   struct rcu_cblist *rclp);

void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq);

bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq);

bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,

				    unsigned long seq);

void rcu_segcblist_merge(struct rcu_segcblist *dst_rsclp,

			 struct rcu_segcblist *src_rsclp);

kernel/rcu/tree.c

+3 −37
Original line number Diff line number Diff line
@@ -708,42 +708,6 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp) 
	return &rsp->node[0];

}



/*

 * Is there any need for future grace periods?

 * Interrupts must be disabled.  If the caller does not hold the root

 * rnp_node structure's ->lock, the results are advisory only.

 */

static int rcu_future_needs_gp(struct rcu_state *rsp)

{

	struct rcu_node *rnp = rcu_get_root(rsp);



	lockdep_assert_irqs_disabled();

	return need_any_future_gp(rnp);

}



/*

 * Does the current CPU require a not-yet-started grace period?

 * The caller must have disabled interrupts to prevent races with

 * normal callback registry.

 */

static bool

cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)

{

	lockdep_assert_irqs_disabled();

	if (rcu_gp_in_progress(rsp))

		return false;  /* No, a grace period is already in progress. */

	if (rcu_future_needs_gp(rsp))

		return true;  /* Yes, a no-CBs CPU needs one. */

	if (!rcu_segcblist_is_enabled(&rdp->cblist))

		return false;  /* No, this is a no-CBs (or offline) CPU. */

	if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))

		return true;  /* Yes, CPU has newly registered callbacks. */

	if (rcu_segcblist_future_gp_needed(&rdp->cblist,

					   READ_ONCE(rsp->completed)))

		return true;  /* Yes, CBs for future grace period. */

	return false; /* No grace period needed. */

}



/*

 * Enter an RCU extended quiescent state, which can be either the

 * idle loop or adaptive-tickless usermode execution.
@@ -3298,7 +3262,9 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) 
		return 1;



	/* Has RCU gone idle with this CPU needing another grace period? */

	if (cpu_needs_another_gp(rsp, rdp))

	if (!rcu_gp_in_progress(rsp) &&

	    rcu_segcblist_is_enabled(&rdp->cblist) &&

	    !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))

		return 1;



	/* Has another RCU grace period completed?  */