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rcu: Avoid having just-onlined CPU resched itself when RCU is idle

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CPUs set rdp->qs_pending when coming online to resolve races with
grace-period start.  However, this means that if RCU is idle, the
just-onlined CPU might needlessly send itself resched IPIs.  Adjust
the online-CPU initialization to avoid this, and also to correctly
cause the CPU to respond to the current grace period if needed.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Josh Boyer <jwboyer@redhat.com>
Tested-by: Christian Hoffmann <email@christianhoffmann.info>
This commit is contained in:
Paul E. McKenney 2011-08-14 15:56:54 -07:00
parent 9bc8b5586f
commit 06ae115a1d
1 changed files with 8 additions and 3 deletions
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11
kernel/rcutree.c
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@ -1911,8 +1911,6 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
/* Set up local state, ensuring consistent view of global state. */
raw_spin_lock_irqsave(&rnp->lock, flags);
rdp->passed_quiesce = 0; /* We could be racing with new GP, */
rdp->qs_pending = 1; /* so set up to respond to current GP. */
rdp->beenonline = 1; /* We have now been online. */
rdp->preemptible = preemptible;
rdp->qlen_last_fqs_check = 0;
@ -1937,8 +1935,15 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
rnp->qsmaskinit |= mask;
mask = rnp->grpmask;
if (rnp == rdp->mynode) {
rdp->gpnum = rnp->completed; /* if GP in progress... */
/*
* If there is a grace period in progress, we will
* set up to wait for it next time we run the
* RCU core code.
*/
rdp->gpnum = rnp->completed;
rdp->completed = rnp->completed;
rdp->passed_quiesce = 0;
rdp->qs_pending = 0;
rdp->passed_quiesce_gpnum = rnp->gpnum - 1;
trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpuonl");
}