Commit-ID: 755609a9087fa983f567dc5452b2fa7b089b591f
Gitweb: http://git.kernel.org/tip/755609a9087fa983f567dc5452b2fa7b089b591f
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Tue, 19 Jun 2012 17:18:20 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Sun, 23 Sep 2012 07:41:52 -0700
rcu: Allow RCU grace-period initialization to be preempted
RCU grace-period initialization is currently carried out with interrupts
disabled, which can result in 200-microsecond latency spikes on systems
on which RCU has been configured for 4096 CPUs. This patch therefore
makes the RCU grace-period initialization be preemptible, which should
eliminate those latency spikes. Similar spikes from grace-period cleanup
and the forcing of quiescent states will be dealt with similarly by later
patches.
Reported-by: Mike Galbraith <mgalbraith@xxxxxxx>
Reported-by: Dimitri Sivanich <sivanich@xxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
---
kernel/rcutree.c | 26 +++++++++++---------------
1 files changed, 11 insertions(+), 15 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index e7a5344..781e5f0 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1030,7 +1030,7 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat
/*
* Body of kthread that handles grace periods.
*/
-static int rcu_gp_kthread(void *arg)
+static int __noreturn rcu_gp_kthread(void *arg)
{
struct rcu_data *rdp;
struct rcu_node *rnp;
@@ -1056,6 +1056,7 @@ static int rcu_gp_kthread(void *arg)
* don't start another one.
*/
raw_spin_unlock_irq(&rnp->lock);
+ cond_resched();
continue;
}
@@ -1066,6 +1067,7 @@ static int rcu_gp_kthread(void *arg)
*/
rsp->fqs_need_gp = 1;
raw_spin_unlock_irq(&rnp->lock);
+ cond_resched();
continue;
}
@@ -1076,10 +1078,10 @@ static int rcu_gp_kthread(void *arg)
rsp->fqs_state = RCU_GP_INIT; /* Stop force_quiescent_state. */
rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
record_gp_stall_check_time(rsp);
- raw_spin_unlock(&rnp->lock); /* leave irqs disabled. */
+ raw_spin_unlock_irq(&rnp->lock);
/* Exclude any concurrent CPU-hotplug operations. */
- raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */
+ get_online_cpus();
/*
* Set the quiescent-state-needed bits in all the rcu_node
@@ -1091,15 +1093,9 @@ static int rcu_gp_kthread(void *arg)
* indicate that no grace period is in progress, at least
* until the corresponding leaf node has been initialized.
* In addition, we have excluded CPU-hotplug operations.
- *
- * Note that the grace period cannot complete until
- * we finish the initialization process, as there will
- * be at least one qsmask bit set in the root node until
- * that time, namely the one corresponding to this CPU,
- * due to the fact that we have irqs disabled.
*/
rcu_for_each_node_breadth_first(rsp, rnp) {
- raw_spin_lock(&rnp->lock); /* irqs already disabled. */
+ raw_spin_lock_irq(&rnp->lock);
rcu_preempt_check_blocked_tasks(rnp);
rnp->qsmask = rnp->qsmaskinit;
rnp->gpnum = rsp->gpnum;
@@ -1110,17 +1106,17 @@ static int rcu_gp_kthread(void *arg)
trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
rnp->level, rnp->grplo,
rnp->grphi, rnp->qsmask);
- raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
+ raw_spin_unlock_irq(&rnp->lock);
+ cond_resched();
}
rnp = rcu_get_root(rsp);
- raw_spin_lock(&rnp->lock); /* irqs already disabled. */
+ raw_spin_lock_irq(&rnp->lock);
/* force_quiescent_state() now OK. */
rsp->fqs_state = RCU_SIGNAL_INIT;
- raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
- raw_spin_unlock_irq(&rsp->onofflock);
+ raw_spin_unlock_irq(&rnp->lock);
+ put_online_cpus();
}
- return 0;
}
/*
--
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