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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>
This commit is contained in:
Paul E. McKenney 2010-12-10 15:02:47 -08:00
parent 5ff8e6f053
commit 121dfc4b3e
1 changed files with 18 additions and 9 deletions
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27
kernel/rcutree.c
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@ -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) {
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 @@ __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;
}
}