On Wed, 18 Mar 2020 17:10:47 -0700 paulmck@xxxxxxxxxx wrote: > From: "Paul E. McKenney" <paulmck@xxxxxxxxxx> > > This commit adds a "rude" variant of RCU-tasks that has as quiescent > states schedule(), cond_resched_tasks_rcu_qs(), userspace execution, > and (in theory, anyway) cond_resched(). In other words, RCU-tasks rude > readers are regions of code with preemption disabled, but excluding code > early in the CPU-online sequence and late in the CPU-offline sequence. > Updates make use of IPIs and force an IPI and a context switch on each > online CPU. This variant is useful in some situations in tracing. > > Suggested-by: Steven Rostedt <rostedt@xxxxxxxxxxx> > [ paulmck: Apply EXPORT_SYMBOL_GPL() feedback from Qiujun Huang. ] > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > --- > include/linux/rcupdate.h | 3 ++ > kernel/rcu/Kconfig | 12 +++++- > kernel/rcu/tasks.h | 98 ++++++++++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 112 insertions(+), 1 deletion(-) > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index 5523145..2be97a8 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -37,6 +37,7 @@ > /* Exported common interfaces */ > void call_rcu(struct rcu_head *head, rcu_callback_t func); > void rcu_barrier_tasks(void); > +void rcu_barrier_tasks_rude(void); > void synchronize_rcu(void); > > #ifdef CONFIG_PREEMPT_RCU > @@ -138,6 +139,8 @@ static inline void rcu_init_nohz(void) { } > #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t) > void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); > void synchronize_rcu_tasks(void); > +void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func); > +void synchronize_rcu_tasks_rude(void); > void exit_tasks_rcu_start(void); > void exit_tasks_rcu_finish(void); > #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ > diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig > index 38475d0..0d43ec1 100644 > --- a/kernel/rcu/Kconfig > +++ b/kernel/rcu/Kconfig > @@ -71,7 +71,7 @@ config TREE_SRCU > This option selects the full-fledged version of SRCU. > > config TASKS_RCU_GENERIC > - def_bool TASKS_RCU > + def_bool TASKS_RCU || TASKS_RUDE_RCU > select SRCU > help > This option enables generic infrastructure code supporting > @@ -84,6 +84,16 @@ config TASKS_RCU > only voluntary context switch (not preemption!), idle, and > user-mode execution as quiescent states. Not for manual selection. > > +config TASKS_RUDE_RCU > + def_bool 0 > + default n No need for "default n" as that's the default without it. > + help > + This option enables a task-based RCU implementation that uses > + only context switch (including preemption) and user-mode > + execution as quiescent states. It forces IPIs and context > + switches on all online CPUs, including idle ones, so use > + with caution. Not for manual selection. Really don't need the "Not for manual selection", as not having a prompt shows that too. > + > config RCU_STALL_COMMON > def_bool TREE_RCU > help > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h > index d77921e..7ba1730 100644 > --- a/kernel/rcu/tasks.h > +++ b/kernel/rcu/tasks.h > @@ -180,6 +180,9 @@ static void __init rcu_tasks_bootup_oddness(void) > else > pr_info("\tTasks RCU enabled.\n"); > #endif /* #ifdef CONFIG_TASKS_RCU */ > +#ifdef CONFIG_TASKS_RUDE_RCU > + pr_info("\tRude variant of Tasks RCU enabled.\n"); > +#endif /* #ifdef CONFIG_TASKS_RUDE_RCU */ > } > > #endif /* #ifndef CONFIG_TINY_RCU */ > @@ -410,3 +413,98 @@ static int __init rcu_spawn_tasks_kthread(void) > core_initcall(rcu_spawn_tasks_kthread); > > #endif /* #ifdef CONFIG_TASKS_RCU */ > + > +#ifdef CONFIG_TASKS_RUDE_RCU > + > +//////////////////////////////////////////////////////////////////////// > +// > +// "Rude" variant of Tasks RCU, inspired by Steve Rostedt's trick of > +// passing an empty function to schedule_on_each_cpu(). This approach > +// provides an asynchronous call_rcu_rude() API and batching of concurrent > +// calls to the synchronous synchronize_rcu_rude() API. This sends IPIs > +// far and wide and induces otherwise unnecessary context switches on all > +// online CPUs, whether online or not. "on all online CPUs, whether online or not" ???? -- Steve > + > +// Empty function to allow workqueues to force a context switch. > +static void rcu_tasks_be_rude(struct work_struct *work) > +{ > +} > +