From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de,
peterz@infradead.org, rostedt@goodmis.org,
Valdis.Kletnieks@vt.edu, dhowells@redhat.com,
eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com,
sbw@mit.edu, patches@linaro.org,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 01/23] rcu: Move RCU grace-period initialization into a kthread
Date: Thu, 20 Sep 2012 11:47:57 -0700 [thread overview]
Message-ID: <1348166900-18716-1-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <20120920184751.GA18657@linux.vnet.ibm.com>
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
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>
---
kernel/rcutree.c | 190 ++++++++++++++++++++++++++++++++++++------------------
kernel/rcutree.h | 3 +
2 files changed, 129 insertions(+), 64 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index f280e54..5b4b093 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1040,6 +1040,102 @@ 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
@@ -1056,77 +1152,20 @@ 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);
}
/*
@@ -2627,6 +2666,28 @@ 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
@@ -2727,6 +2788,7 @@ 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)
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 4d29169..117a150 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -385,6 +385,9 @@ struct rcu_state {
u8 boost; /* Subject to priority boost. */
unsigned long gpnum; /* Current gp number. */
unsigned long completed; /* # of last completed gp. */
+ struct task_struct *gp_kthread; /* Task for grace periods. */
+ wait_queue_head_t gp_wq; /* Where GP task waits. */
+ int gp_flags; /* Commands for GP task. */
/* End of fields guarded by root rcu_node's lock. */
--
1.7.8
next prev parent reply other threads:[~2012-09-20 18:50 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-20 18:47 [PATCH tip/core/rcu 0/23] v2 Improvements to RT response on big systems and expedited functions Paul E. McKenney
2012-09-20 18:47 ` Paul E. McKenney [this message]
2012-09-20 18:47 ` [PATCH tip/core/rcu 02/23] rcu: Prevent initialization-time quiescent-state race Paul E. McKenney
2012-09-20 18:47 ` [PATCH tip/core/rcu 03/23] rcu: Allow RCU grace-period initialization to be preempted Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 04/23] rcu: Move RCU grace-period cleanup into kthread Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 05/23] rcu: Allow RCU grace-period cleanup to be preempted Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 06/23] rcu: Break up rcu_gp_kthread() into subfunctions Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 07/23] rcu: Prevent offline CPUs from executing RCU core code Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 08/23] rcu: Provide OOM handler to motivate lazy RCU callbacks Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 09/23] rcu: Segregate rcu_state fields to improve cache locality Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 10/23] rcu: Move quiescent-state forcing into kthread Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 11/23] rcu: Allow RCU quiescent-state forcing to be preempted Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 12/23] rcu: Adjust debugfs tracing for kthread-based quiescent-state forcing Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 13/23] rcu: Prevent force_quiescent_state() memory contention Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 14/23] rcu: Control grace-period duration from sysfs Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 15/23] rcu: Make rcutree module parameters visible in sysfs Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 16/23] rcu: Fix day-zero grace-period initialization/cleanup race Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 17/23] rcu: Add random PROVE_RCU_DELAY to grace-period initialization Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 18/23] rcu: Adjust for unconditional ->completed assignment Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 19/23] rcu: Eliminate signed overflow in synchronize_rcu_expedited() Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 20/23] rcu: Reduce synchronize_rcu_expedited() latency Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 21/23] rcu: Simplify quiescent-state detection Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 22/23] rcu: Handle unbalanced rcu_node configurations with few CPUs Paul E. McKenney
2012-09-20 18:48 ` [PATCH tip/core/rcu 23/23] rcu: Shrink RCU based on number of CPUs Paul E. McKenney
-- strict thread matches above, loose matches on Subject: below --
2012-08-30 18:18 [PATCH tip/core/rcu 0/23] Improvements to RT response on big systems and expedited functions Paul E. McKenney
2012-08-30 18:18 ` [PATCH tip/core/rcu 01/23] rcu: Move RCU grace-period initialization into a kthread Paul E. McKenney
2012-09-02 1:04 ` Josh Triplett
2012-09-06 13:32 ` Peter Zijlstra
2012-09-06 17:00 ` Paul E. McKenney
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