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: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 8105271..c39ec5b 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -617,9 +617,17 @@
static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
{
if (rdp->gpnum != rnp->gpnum) {
- rdp->qs_pending = 1;
- rdp->passed_quiesc = 0;
+ /*
+ * 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;
+ } else
+ rdp->qs_pending = 0;
}
}
@@ -681,19 +689,20 @@
/*
* 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;
}
}
