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Commit 46a1e34e authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Ingo Molnar
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rcu: Make force_quiescent_state() start grace period if needed 



Grace periods cannot be started while force_quiescent_state() is
active.  This is OK in that the affected CPUs will try again
later, but it does induce needless grace-period delays.  This
patch causes rcu_start_gp() to record a failed attempt to start
a grace period. When force_quiescent_state() prepares to return,
it then starts the grace period if there was such a failed
attempt.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12626465501854-git-send-email->
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 45f014c5

kernel/rcutree.c

+8 −0
Original line number Diff line number Diff line
@@ -660,6 +660,8 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) 
	struct rcu_node *rnp = rcu_get_root(rsp);



	if (!cpu_needs_another_gp(rsp, rdp) || rsp->fqs_active) {

		if (cpu_needs_another_gp(rsp, rdp))

			rsp->fqs_need_gp = 1;

		if (rnp->completed == rsp->completed) {

			spin_unlock_irqrestore(&rnp->lock, flags);

			return;
@@ -1239,6 +1241,12 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) 
		break;

	}

	rsp->fqs_active = 0;

	if (rsp->fqs_need_gp) {

		spin_unlock(&rsp->fqslock); /* irqs remain disabled */

		rsp->fqs_need_gp = 0;

		rcu_start_gp(rsp, flags); /* releases rnp->lock */

		return;

	}

	spin_unlock(&rnp->lock);  /* irqs remain disabled */

unlock_fqs_ret:

	spin_unlock_irqrestore(&rsp->fqslock, flags);

kernel/rcutree.h

+5 −0
Original line number Diff line number Diff line
@@ -278,6 +278,11 @@ struct rcu_state { 
						/* Force QS state. */

	u8	fqs_active;			/* force_quiescent_state() */

						/*  is running. */

	u8	fqs_need_gp;			/* A CPU was prevented from */

						/*  starting a new grace */

						/*  period because */

						/*  force_quiescent_state() */

						/*  was running. */

	long	gpnum;				/* Current gp number. */

	long	completed;			/* # of last completed gp. */