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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-06-18 18:36:08 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-09-23 07:41:52 -0700
commitb3dbec76e5334fbb063987dea14e7b255602d7e4 (patch)
tree5b75e737856baf09b2303bebf7d9893b8279c84e /kernel/rcutree.c
parenta10d206ef1a83121ab7430cb196e0376a7145b22 (diff)
downloadop-kernel-dev-b3dbec76e5334fbb063987dea14e7b255602d7e4.zip
op-kernel-dev-b3dbec76e5334fbb063987dea14e7b255602d7e4.tar.gz
rcu: Move RCU grace-period initialization into a kthread
As the first step towards allowing grace-period initialization to be preemptible, this commit moves the RCU grace-period initialization into its own kthread. This is needed to keep large-system scheduling latency at reasonable levels. Also change raw_spin_lock_irqsave() to raw_spin_lock_irq() as suggested by Peter Zijlstra in review comments. Reported-by: Mike Galbraith <mgalbraith@suse.de> Reported-by: Dimitri Sivanich <sivanich@sgi.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Diffstat (limited to 'kernel/rcutree.c')
-rw-r--r--kernel/rcutree.c190
1 files changed, 126 insertions, 64 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index f7bcd9e..4792f16 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1042,6 +1042,102 @@ 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)
+{
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+ struct rcu_state *rsp = arg;
+
+ for (;;) {
+
+ /* Handle grace-period start. */
+ rnp = rcu_get_root(rsp);
+ for (;;) {
+ wait_event_interruptible(rsp->gp_wq, rsp->gp_flags);
+ if (rsp->gp_flags)
+ break;
+ flush_signals(current);
+ }
+ raw_spin_lock_irq(&rnp->lock);
+ rsp->gp_flags = 0;
+ rdp = this_cpu_ptr(rsp->rda);
+
+ if (rcu_gp_in_progress(rsp)) {
+ /*
+ * A grace period is already in progress, so
+ * don't start another one.
+ */
+ raw_spin_unlock_irq(&rnp->lock);
+ continue;
+ }
+
+ if (rsp->fqs_active) {
+ /*
+ * We need a grace period, but force_quiescent_state()
+ * is running. Tell it to start one on our behalf.
+ */
+ rsp->fqs_need_gp = 1;
+ raw_spin_unlock_irq(&rnp->lock);
+ continue;
+ }
+
+ /* Advance to a new grace period and initialize state. */
+ rsp->gpnum++;
+ trace_rcu_grace_period(rsp->name, rsp->gpnum, "start");
+ WARN_ON_ONCE(rsp->fqs_state == RCU_GP_INIT);
+ 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. */
+
+ /* Exclude any concurrent CPU-hotplug operations. */
+ raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */
+
+ /*
+ * Set the quiescent-state-needed bits in all the rcu_node
+ * structures for all currently online CPUs in breadth-first
+ * order, starting from the root rcu_node structure.
+ * This operation relies on the layout of the hierarchy
+ * within the rsp->node[] array. Note that other CPUs will
+ * access only the leaves of the hierarchy, which still
+ * 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. */
+ rcu_preempt_check_blocked_tasks(rnp);
+ rnp->qsmask = rnp->qsmaskinit;
+ rnp->gpnum = rsp->gpnum;
+ rnp->completed = rsp->completed;
+ if (rnp == rdp->mynode)
+ rcu_start_gp_per_cpu(rsp, rnp, rdp);
+ rcu_preempt_boost_start_gp(rnp);
+ 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. */
+ }
+
+ rnp = rcu_get_root(rsp);
+ raw_spin_lock(&rnp->lock); /* irqs already disabled. */
+ /* 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);
+ }
+ return 0;
+}
+
+/*
* Start a new RCU grace period if warranted, re-initializing the hierarchy
* in preparation for detecting the next grace period. The caller must hold
* the root node's ->lock, which is released before return. Hard irqs must
@@ -1058,77 +1154,20 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
struct rcu_node *rnp = rcu_get_root(rsp);
- if (!rcu_scheduler_fully_active ||
+ if (!rsp->gp_kthread ||
!cpu_needs_another_gp(rsp, rdp)) {
/*
- * Either the scheduler hasn't yet spawned the first
- * non-idle task or this CPU does not need another
- * grace period. Either way, don't start a new grace
- * period.
+ * Either we have not yet spawned the grace-period
+ * task or this CPU does not need another grace period.
+ * Either way, don't start a new grace period.
*/
raw_spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
- if (rsp->fqs_active) {
- /*
- * This CPU needs a grace period, but force_quiescent_state()
- * is running. Tell it to start one on this CPU's behalf.
- */
- rsp->fqs_need_gp = 1;
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- return;
- }
-
- /* Advance to a new grace period and initialize state. */
- rsp->gpnum++;
- trace_rcu_grace_period(rsp->name, rsp->gpnum, "start");
- WARN_ON_ONCE(rsp->fqs_state == RCU_GP_INIT);
- rsp->fqs_state = RCU_GP_INIT; /* Hold off 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. */
-
- /* Exclude any concurrent CPU-hotplug operations. */
- raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */
-
- /*
- * Set the quiescent-state-needed bits in all the rcu_node
- * structures for all currently online CPUs in breadth-first
- * order, starting from the root rcu_node structure. This
- * operation relies on the layout of the hierarchy within the
- * rsp->node[] array. Note that other CPUs will access only
- * the leaves of the hierarchy, which still 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. */
- rcu_preempt_check_blocked_tasks(rnp);
- rnp->qsmask = rnp->qsmaskinit;
- rnp->gpnum = rsp->gpnum;
- rnp->completed = rsp->completed;
- if (rnp == rdp->mynode)
- rcu_start_gp_per_cpu(rsp, rnp, rdp);
- rcu_preempt_boost_start_gp(rnp);
- 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. */
- }
-
- rnp = rcu_get_root(rsp);
- raw_spin_lock(&rnp->lock); /* irqs already disabled. */
- rsp->fqs_state = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */
- raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
- raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
+ rsp->gp_flags = 1;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ wake_up(&rsp->gp_wq);
}
/*
@@ -2629,6 +2668,28 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
}
/*
+ * Spawn the kthread that handles this RCU flavor's grace periods.
+ */
+static int __init rcu_spawn_gp_kthread(void)
+{
+ unsigned long flags;
+ struct rcu_node *rnp;
+ struct rcu_state *rsp;
+ struct task_struct *t;
+
+ for_each_rcu_flavor(rsp) {
+ t = kthread_run(rcu_gp_kthread, rsp, rsp->name);
+ BUG_ON(IS_ERR(t));
+ rnp = rcu_get_root(rsp);
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ rsp->gp_kthread = t;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ }
+ return 0;
+}
+early_initcall(rcu_spawn_gp_kthread);
+
+/*
* This function is invoked towards the end of the scheduler's initialization
* process. Before this is called, the idle task might contain
* RCU read-side critical sections (during which time, this idle
@@ -2729,6 +2790,7 @@ static void __init rcu_init_one(struct rcu_state *rsp,
}
rsp->rda = rda;
+ init_waitqueue_head(&rsp->gp_wq);
rnp = rsp->level[rcu_num_lvls - 1];
for_each_possible_cpu(i) {
while (i > rnp->grphi)
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