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Commit 121dfc4b authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: fine-tune grace-period begin/end checks 



Use the CPU's bit in rnp->qsmask to determine whether or not the CPU
should try to report a quiescent state.  Handle overflow in the check
for rdp->gpnum having fallen behind.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 5ff8e6f0

kernel/rcutree.c

+18 −9
Original line number Diff line number Diff line
@@ -617,9 +617,17 @@ static void __init check_cpu_stall_init(void) 
static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)

{

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

		/*

		 * If the current grace period is waiting for this CPU,

		 * set up to detect a quiescent state, otherwise don't

		 * go looking for one.

		 */

		rdp->gpnum = rnp->gpnum;

		if (rnp->qsmask & rdp->grpmask) {

			rdp->qs_pending = 1;

			rdp->passed_quiesc = 0;

		rdp->gpnum = rnp->gpnum;

		} else

			rdp->qs_pending = 0;

	}

}
@@ -681,19 +689,20 @@ __rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat 


		/*

		 * If we were in an extended quiescent state, we may have

		 * missed some grace periods that others CPUs took care on

		 * missed some grace periods that others CPUs handled on

		 * our behalf. Catch up with this state to avoid noting

		 * spurious new grace periods.

		 * spurious new grace periods.  If another grace period

		 * has started, then rnp->gpnum will have advanced, so

		 * we will detect this later on.

		 */

		if (rdp->completed > rdp->gpnum)

		if (ULONG_CMP_LT(rdp->gpnum, rdp->completed))

			rdp->gpnum = rdp->completed;



		/*

		 * If another CPU handled our extended quiescent states and

		 * we have no more grace period to complete yet, then stop

		 * chasing quiescent states.

		 * If RCU does not need a quiescent state from this CPU,

		 * then make sure that this CPU doesn't go looking for one.

		 */

		if (rdp->completed == rnp->gpnum)

		if ((rnp->qsmask & rdp->grpmask) == 0)

			rdp->qs_pending = 0;

	}

}