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authorSebastian Andrzej Siewior <bigeasy@linutronix.de>2019-03-20 22:13:33 +0100
committerPaul E. McKenney <paulmck@linux.ibm.com>2019-05-25 14:50:46 -0700
commit48d07c04b4cc1dc1221965312f58fd84926212fe (patch)
treef70300d26abc17bca3602990cca44f309a2120af /kernel/rcu/tree_plugin.h
parenta188339ca5a396acc588e5851ed7e19f66b0ebd9 (diff)
rcu: Enable elimination of Tree-RCU softirq processing
Some workloads need to change kthread priority for RCU core processing without affecting other softirq work. This commit therefore introduces the rcutree.use_softirq kernel boot parameter, which moves the RCU core work from softirq to a per-CPU SCHED_OTHER kthread named rcuc. Use of SCHED_OTHER approach avoids the scalability problems that appeared with the earlier attempt to move RCU core processing to from softirq to kthreads. That said, kernels built with RCU_BOOST=y will run the rcuc kthreads at the RCU-boosting priority. Note that rcutree.use_softirq=0 must be specified to move RCU core processing to the rcuc kthreads: rcutree.use_softirq=1 is the default. Reported-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Mike Galbraith <efault@gmx.de> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> [ paulmck: Adjust for invoke_rcu_callbacks() only ever being invoked from RCU core processing, in contrast to softirq->rcuc transition in old mainline RCU priority boosting. ] [ paulmck: Avoid wakeups when scheduler might have invoked rcu_read_unlock() while holding rq or pi locks, also possibly fixing a pre-existing latent bug involving raise_softirq()-induced wakeups. ] Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Diffstat (limited to 'kernel/rcu/tree_plugin.h')
-rw-r--r--kernel/rcu/tree_plugin.h134
1 files changed, 14 insertions, 120 deletions
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 1102765f91fd..21611862e083 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -11,29 +11,7 @@
* Paul E. McKenney <paulmck@linux.ibm.com>
*/
-#include <linux/delay.h>
-#include <linux/gfp.h>
-#include <linux/oom.h>
-#include <linux/sched/debug.h>
-#include <linux/smpboot.h>
-#include <linux/sched/isolation.h>
-#include <uapi/linux/sched/types.h>
-#include "../time/tick-internal.h"
-
-#ifdef CONFIG_RCU_BOOST
#include "../locking/rtmutex_common.h"
-#else /* #ifdef CONFIG_RCU_BOOST */
-
-/*
- * Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST,
- * all uses are in dead code. Provide a definition to keep the compiler
- * happy, but add WARN_ON_ONCE() to complain if used in the wrong place.
- * This probably needs to be excluded from -rt builds.
- */
-#define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; })
-#define rt_mutex_futex_unlock(x) WARN_ON_ONCE(1)
-
-#endif /* #else #ifdef CONFIG_RCU_BOOST */
#ifdef CONFIG_RCU_NOCB_CPU
static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
@@ -94,6 +72,8 @@ static void __init rcu_bootup_announce_oddness(void)
pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);
if (gp_cleanup_delay)
pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay);
+ if (!use_softirq)
+ pr_info("\tRCU_SOFTIRQ processing moved to rcuc kthreads.\n");
if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
pr_info("\tRCU debug extended QS entry/exit.\n");
rcupdate_announce_bootup_oddness();
@@ -627,7 +607,7 @@ static void rcu_read_unlock_special(struct task_struct *t)
if (preempt_bh_were_disabled || irqs_were_disabled) {
WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, false);
/* Need to defer quiescent state until everything is enabled. */
- if (irqs_were_disabled) {
+ if (irqs_were_disabled && use_softirq) {
/* Enabling irqs does not reschedule, so... */
raise_softirq_irqoff(RCU_SOFTIRQ);
} else {
@@ -944,18 +924,21 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
+/*
+ * If boosting, set rcuc kthreads to realtime priority.
+ */
+static void rcu_cpu_kthread_setup(unsigned int cpu)
+{
#ifdef CONFIG_RCU_BOOST
+ struct sched_param sp;
-static void rcu_wake_cond(struct task_struct *t, int status)
-{
- /*
- * If the thread is yielding, only wake it when this
- * is invoked from idle
- */
- if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
- wake_up_process(t);
+ sp.sched_priority = kthread_prio;
+ sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
+#endif /* #ifdef CONFIG_RCU_BOOST */
}
+#ifdef CONFIG_RCU_BOOST
+
/*
* Carry out RCU priority boosting on the task indicated by ->exp_tasks
* or ->boost_tasks, advancing the pointer to the next task in the
@@ -1091,23 +1074,6 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
}
/*
- * Wake up the per-CPU kthread to invoke RCU callbacks.
- */
-static void invoke_rcu_callbacks_kthread(void)
-{
- unsigned long flags;
-
- local_irq_save(flags);
- __this_cpu_write(rcu_data.rcu_cpu_has_work, 1);
- if (__this_cpu_read(rcu_data.rcu_cpu_kthread_task) != NULL &&
- current != __this_cpu_read(rcu_data.rcu_cpu_kthread_task)) {
- rcu_wake_cond(__this_cpu_read(rcu_data.rcu_cpu_kthread_task),
- __this_cpu_read(rcu_data.rcu_cpu_kthread_status));
- }
- local_irq_restore(flags);
-}
-
-/*
* Is the current CPU running the RCU-callbacks kthread?
* Caller must have preemption disabled.
*/
@@ -1160,59 +1126,6 @@ static int rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
return 0;
}
-static void rcu_cpu_kthread_setup(unsigned int cpu)
-{
- struct sched_param sp;
-
- sp.sched_priority = kthread_prio;
- sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
-}
-
-static void rcu_cpu_kthread_park(unsigned int cpu)
-{
- per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
-}
-
-static int rcu_cpu_kthread_should_run(unsigned int cpu)
-{
- return __this_cpu_read(rcu_data.rcu_cpu_has_work);
-}
-
-/*
- * Per-CPU kernel thread that invokes RCU callbacks. This replaces
- * the RCU softirq used in configurations of RCU that do not support RCU
- * priority boosting.
- */
-static void rcu_cpu_kthread(unsigned int cpu)
-{
- unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status);
- char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work);
- int spincnt;
-
- for (spincnt = 0; spincnt < 10; spincnt++) {
- trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
- local_bh_disable();
- *statusp = RCU_KTHREAD_RUNNING;
- local_irq_disable();
- work = *workp;
- *workp = 0;
- local_irq_enable();
- if (work)
- rcu_do_batch(this_cpu_ptr(&rcu_data));
- local_bh_enable();
- if (*workp == 0) {
- trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
- *statusp = RCU_KTHREAD_WAITING;
- return;
- }
- }
- *statusp = RCU_KTHREAD_YIELDING;
- trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
- schedule_timeout_interruptible(2);
- trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
- *statusp = RCU_KTHREAD_WAITING;
-}
-
/*
* Set the per-rcu_node kthread's affinity to cover all CPUs that are
* served by the rcu_node in question. The CPU hotplug lock is still
@@ -1243,27 +1156,13 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
free_cpumask_var(cm);
}
-static struct smp_hotplug_thread rcu_cpu_thread_spec = {
- .store = &rcu_data.rcu_cpu_kthread_task,
- .thread_should_run = rcu_cpu_kthread_should_run,
- .thread_fn = rcu_cpu_kthread,
- .thread_comm = "rcuc/%u",
- .setup = rcu_cpu_kthread_setup,
- .park = rcu_cpu_kthread_park,
-};
-
/*
* Spawn boost kthreads -- called as soon as the scheduler is running.
*/
static void __init rcu_spawn_boost_kthreads(void)
{
struct rcu_node *rnp;
- int cpu;
- for_each_possible_cpu(cpu)
- per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0;
- if (WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), "%s: Could not start rcub kthread, OOM is now expected behavior\n", __func__))
- return;
rcu_for_each_leaf_node(rnp)
(void)rcu_spawn_one_boost_kthread(rnp);
}
@@ -1286,11 +1185,6 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
-static void invoke_rcu_callbacks_kthread(void)
-{
- WARN_ON_ONCE(1);
-}
-
static bool rcu_is_callbacks_kthread(void)
{
return false;