From 06ae115a1d551cd952d80df06eaf8b5153351875 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sun, 14 Aug 2011 15:56:54 -0700 Subject: rcu: Avoid having just-onlined CPU resched itself when RCU is idle 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 Tested-by: Josh Boyer Tested-by: Christian Hoffmann diff --git a/kernel/rcutree.c b/kernel/rcutree.c index ade7883..c95fa89 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -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"); } -- cgit v0.10.2