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authorPaul E. McKenney <paul.mckenney@linaro.org>2011-06-18 09:55:39 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-09-28 21:38:20 -0700
commit965a002b4f1a458c5dcb334ec29f48a0046faa25 (patch)
tree9aa3847fd44b322a73631758e7337632e5e3a32d /kernel/rcutiny_plugin.h
parent385680a9487d2f85382ad6d74e2a15837e47bfd9 (diff)
downloadblackbird-op-linux-965a002b4f1a458c5dcb334ec29f48a0046faa25.tar.gz
blackbird-op-linux-965a002b4f1a458c5dcb334ec29f48a0046faa25.zip
rcu: Make TINY_RCU also use softirq for RCU_BOOST=n
This patch #ifdefs TINY_RCU kthreads out of the kernel unless RCU_BOOST=y, thus eliminating context-switch overhead if RCU priority boosting has not been configured. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcutiny_plugin.h')
-rw-r--r--kernel/rcutiny_plugin.h110
1 files changed, 83 insertions, 27 deletions
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 791ddf7c99ab..02aa7139861c 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -245,6 +245,13 @@ static void show_tiny_preempt_stats(struct seq_file *m)
#include "rtmutex_common.h"
+#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
+
+/* Controls for rcu_kthread() kthread. */
+static struct task_struct *rcu_kthread_task;
+static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
+static unsigned long have_rcu_kthread_work;
+
/*
* Carry out RCU priority boosting on the task indicated by ->boost_tasks,
* and advance ->boost_tasks to the next task in the ->blkd_tasks list.
@@ -332,7 +339,7 @@ static int rcu_initiate_boost(void)
if (rcu_preempt_ctrlblk.exp_tasks == NULL)
rcu_preempt_ctrlblk.boost_tasks =
rcu_preempt_ctrlblk.gp_tasks;
- invoke_rcu_kthread();
+ invoke_rcu_callbacks();
} else
RCU_TRACE(rcu_initiate_boost_trace());
return 1;
@@ -351,14 +358,6 @@ static void rcu_preempt_boost_start_gp(void)
#else /* #ifdef CONFIG_RCU_BOOST */
/*
- * If there is no RCU priority boosting, we don't boost.
- */
-static int rcu_boost(void)
-{
- return 0;
-}
-
-/*
* If there is no RCU priority boosting, we don't initiate boosting,
* but we do indicate whether there are blocked readers blocking the
* current grace period.
@@ -425,7 +424,7 @@ static void rcu_preempt_cpu_qs(void)
/* If there are done callbacks, cause them to be invoked. */
if (*rcu_preempt_ctrlblk.rcb.donetail != NULL)
- invoke_rcu_kthread();
+ invoke_rcu_callbacks();
}
/*
@@ -646,7 +645,7 @@ static void rcu_preempt_check_callbacks(void)
rcu_preempt_cpu_qs();
if (&rcu_preempt_ctrlblk.rcb.rcucblist !=
rcu_preempt_ctrlblk.rcb.donetail)
- invoke_rcu_kthread();
+ invoke_rcu_callbacks();
if (rcu_preempt_gp_in_progress() &&
rcu_cpu_blocking_cur_gp() &&
rcu_preempt_running_reader())
@@ -672,7 +671,7 @@ static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
*/
static void rcu_preempt_process_callbacks(void)
{
- rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb);
+ __rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb);
}
/*
@@ -848,15 +847,6 @@ static void show_tiny_preempt_stats(struct seq_file *m)
#endif /* #ifdef CONFIG_RCU_TRACE */
/*
- * Because preemptible RCU does not exist, it is never necessary to
- * boost preempted RCU readers.
- */
-static int rcu_boost(void)
-{
- return 0;
-}
-
-/*
* Because preemptible RCU does not exist, it never has any callbacks
* to check.
*/
@@ -882,6 +872,78 @@ static void rcu_preempt_process_callbacks(void)
#endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */
+#ifdef CONFIG_RCU_BOOST
+
+/*
+ * Wake up rcu_kthread() to process callbacks now eligible for invocation
+ * or to boost readers.
+ */
+static void invoke_rcu_callbacks(void)
+{
+ have_rcu_kthread_work = 1;
+ wake_up(&rcu_kthread_wq);
+}
+
+/*
+ * This kthread invokes RCU callbacks whose grace periods have
+ * elapsed. It is awakened as needed, and takes the place of the
+ * RCU_SOFTIRQ that is used for this purpose when boosting is disabled.
+ * This is a kthread, but it is never stopped, at least not until
+ * the system goes down.
+ */
+static int rcu_kthread(void *arg)
+{
+ unsigned long work;
+ unsigned long morework;
+ unsigned long flags;
+
+ for (;;) {
+ wait_event_interruptible(rcu_kthread_wq,
+ have_rcu_kthread_work != 0);
+ morework = rcu_boost();
+ local_irq_save(flags);
+ work = have_rcu_kthread_work;
+ have_rcu_kthread_work = morework;
+ local_irq_restore(flags);
+ if (work)
+ rcu_process_callbacks(NULL);
+ schedule_timeout_interruptible(1); /* Leave CPU for others. */
+ }
+
+ return 0; /* Not reached, but needed to shut gcc up. */
+}
+
+/*
+ * Spawn the kthread that invokes RCU callbacks.
+ */
+static int __init rcu_spawn_kthreads(void)
+{
+ struct sched_param sp;
+
+ rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread");
+ sp.sched_priority = RCU_BOOST_PRIO;
+ sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp);
+ return 0;
+}
+early_initcall(rcu_spawn_kthreads);
+
+#else /* #ifdef CONFIG_RCU_BOOST */
+
+/*
+ * Start up softirq processing of callbacks.
+ */
+void invoke_rcu_callbacks(void)
+{
+ raise_softirq(RCU_SOFTIRQ);
+}
+
+void rcu_init(void)
+{
+ open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+}
+
+#endif /* #else #ifdef CONFIG_RCU_BOOST */
+
#ifdef CONFIG_DEBUG_LOCK_ALLOC
#include <linux/kernel_stat.h>
@@ -897,12 +959,6 @@ void __init rcu_scheduler_starting(void)
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
-#ifdef CONFIG_RCU_BOOST
-#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
-#else /* #ifdef CONFIG_RCU_BOOST */
-#define RCU_BOOST_PRIO 1
-#endif /* #else #ifdef CONFIG_RCU_BOOST */
-
#ifdef CONFIG_RCU_TRACE
#ifdef CONFIG_RCU_BOOST
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