diff options
Diffstat (limited to 'debian/patches-rt/0160-rcu-Eliminate-softirq-processing-from-rcutree.patch')
| -rw-r--r-- | debian/patches-rt/0160-rcu-Eliminate-softirq-processing-from-rcutree.patch | 423 |
1 files changed, 423 insertions, 0 deletions
diff --git a/debian/patches-rt/0160-rcu-Eliminate-softirq-processing-from-rcutree.patch b/debian/patches-rt/0160-rcu-Eliminate-softirq-processing-from-rcutree.patch new file mode 100644 index 000000000..d4a6e3195 --- /dev/null +++ b/debian/patches-rt/0160-rcu-Eliminate-softirq-processing-from-rcutree.patch @@ -0,0 +1,423 @@ +From 4fa514eb294144f8698e721f4b5a4de0447be272 Mon Sep 17 00:00:00 2001 +From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> +Date: Mon, 4 Nov 2013 13:21:10 -0800 +Subject: [PATCH 160/347] rcu: Eliminate softirq processing from rcutree +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.246-rt110.tar.xz + +Running RCU out of softirq is a problem for some workloads that would +like to manage RCU core processing independently of other softirq work, +for example, setting kthread priority. This commit therefore moves the +RCU core work from softirq to a per-CPU/per-flavor SCHED_OTHER kthread +named rcuc. The 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. + +Reported-by: Thomas Gleixner <tglx@linutronix.de> +Tested-by: Mike Galbraith <bitbucket@online.de> +Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + kernel/rcu/tree.c | 114 ++++++++++++++++++++++++++++--- + kernel/rcu/tree.h | 4 +- + kernel/rcu/tree_plugin.h | 142 +++------------------------------------ + 3 files changed, 115 insertions(+), 145 deletions(-) + +diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c +index 1a40e3d44cb8..ae716ca783bc 100644 +--- a/kernel/rcu/tree.c ++++ b/kernel/rcu/tree.c +@@ -61,6 +61,13 @@ + #include <linux/trace_events.h> + #include <linux/suspend.h> + #include <linux/ftrace.h> ++#include <linux/delay.h> ++#include <linux/gfp.h> ++#include <linux/oom.h> ++#include <linux/smpboot.h> ++#include <linux/jiffies.h> ++#include <linux/sched/isolation.h> ++#include "../time/tick-internal.h" + + #include "tree.h" + #include "rcu.h" +@@ -2896,18 +2903,17 @@ __rcu_process_callbacks(struct rcu_state *rsp) + /* + * Do RCU core processing for the current CPU. + */ +-static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused) ++static __latent_entropy void rcu_process_callbacks(void) + { + struct rcu_state *rsp; + + if (cpu_is_offline(smp_processor_id())) + return; +- trace_rcu_utilization(TPS("Start RCU core")); + for_each_rcu_flavor(rsp) + __rcu_process_callbacks(rsp); +- trace_rcu_utilization(TPS("End RCU core")); + } + ++static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task); + /* + * Schedule RCU callback invocation. If the specified type of RCU + * does not support RCU priority boosting, just do a direct call, +@@ -2919,18 +2925,105 @@ static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp) + { + if (unlikely(!READ_ONCE(rcu_scheduler_fully_active))) + return; +- if (likely(!rsp->boost)) { +- rcu_do_batch(rsp, rdp); +- return; +- } +- invoke_rcu_callbacks_kthread(); ++ rcu_do_batch(rsp, rdp); ++} ++ ++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 (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current))) ++ wake_up_process(t); + } + ++/* ++ * Wake up this CPU's rcuc kthread to do RCU core processing. ++ */ + static void invoke_rcu_core(void) + { +- if (cpu_online(smp_processor_id())) +- raise_softirq(RCU_SOFTIRQ); ++ unsigned long flags; ++ struct task_struct *t; ++ ++ if (!cpu_online(smp_processor_id())) ++ return; ++ local_irq_save(flags); ++ __this_cpu_write(rcu_cpu_has_work, 1); ++ t = __this_cpu_read(rcu_cpu_kthread_task); ++ if (t != NULL && current != t) ++ rcu_wake_cond(t, __this_cpu_read(rcu_cpu_kthread_status)); ++ local_irq_restore(flags); ++} ++ ++static void rcu_cpu_kthread_park(unsigned int cpu) ++{ ++ per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; ++} ++ ++static int rcu_cpu_kthread_should_run(unsigned int cpu) ++{ ++ return __this_cpu_read(rcu_cpu_has_work); ++} ++ ++/* ++ * Per-CPU kernel thread that invokes RCU callbacks. This replaces the ++ * RCU softirq used in flavors and 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_cpu_kthread_status); ++ char work, *workp = this_cpu_ptr(&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; ++ this_cpu_inc(rcu_cpu_kthread_loops); ++ local_irq_disable(); ++ work = *workp; ++ *workp = 0; ++ local_irq_enable(); ++ if (work) ++ rcu_process_callbacks(); ++ 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; ++} ++ ++static struct smp_hotplug_thread rcu_cpu_thread_spec = { ++ .store = &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 per-CPU RCU core processing kthreads. ++ */ ++static int __init rcu_spawn_core_kthreads(void) ++{ ++ int cpu; ++ ++ for_each_possible_cpu(cpu) ++ per_cpu(rcu_cpu_has_work, cpu) = 0; ++ BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec)); ++ return 0; + } ++early_initcall(rcu_spawn_core_kthreads); + + /* + * Handle any core-RCU processing required by a call_rcu() invocation. +@@ -4196,7 +4289,6 @@ void __init rcu_init(void) + if (dump_tree) + rcu_dump_rcu_node_tree(&rcu_sched_state); + __rcu_init_preempt(); +- open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); + + /* + * We don't need protection against CPU-hotplug here because +diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h +index fbbff7c21148..98257d20feb2 100644 +--- a/kernel/rcu/tree.h ++++ b/kernel/rcu/tree.h +@@ -423,12 +423,10 @@ extern struct rcu_state rcu_preempt_state; + + int rcu_dynticks_snap(struct rcu_dynticks *rdtp); + +-#ifdef CONFIG_RCU_BOOST + DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status); + DECLARE_PER_CPU(int, rcu_cpu_kthread_cpu); + DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_loops); + DECLARE_PER_CPU(char, rcu_cpu_has_work); +-#endif /* #ifdef CONFIG_RCU_BOOST */ + + #ifndef RCU_TREE_NONCORE + +@@ -451,8 +449,8 @@ static void dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, + int ncheck); + static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags); + static void rcu_preempt_boost_start_gp(struct rcu_node *rnp); +-static void invoke_rcu_callbacks_kthread(void); + static bool rcu_is_callbacks_kthread(void); ++static void rcu_cpu_kthread_setup(unsigned int cpu); + #ifdef CONFIG_RCU_BOOST + static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp, + struct rcu_node *rnp); +diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h +index 938e64c69d18..56639c8ed550 100644 +--- a/kernel/rcu/tree_plugin.h ++++ b/kernel/rcu/tree_plugin.h +@@ -24,42 +24,16 @@ + * Paul E. McKenney <paulmck@linux.vnet.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/jiffies.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" + + /* + * Control variables for per-CPU and per-rcu_node kthreads. These + * handle all flavors of RCU. + */ +-static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task); + DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status); + DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops); + DEFINE_PER_CPU(char, rcu_cpu_has_work); + +-#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. */ + static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ +@@ -1028,18 +1002,21 @@ dump_blkd_tasks(struct rcu_state *rsp, 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 +@@ -1177,23 +1154,6 @@ 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_cpu_has_work, 1); +- if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && +- current != __this_cpu_read(rcu_cpu_kthread_task)) { +- rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), +- __this_cpu_read(rcu_cpu_kthread_status)); +- } +- local_irq_restore(flags); +-} +- + /* + * Is the current CPU running the RCU-callbacks kthread? + * Caller must have preemption disabled. +@@ -1248,67 +1208,6 @@ static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp, + return 0; + } + +-static void rcu_kthread_do_work(void) +-{ +- rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data)); +- rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data)); +- rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data)); +-} +- +-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_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; +-} +- +-static int rcu_cpu_kthread_should_run(unsigned int cpu) +-{ +- return __this_cpu_read(rcu_cpu_has_work); +-} +- +-/* +- * Per-CPU kernel thread that invokes RCU callbacks. This replaces the +- * RCU softirq used in flavors and 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_cpu_kthread_status); +- char work, *workp = this_cpu_ptr(&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; +- this_cpu_inc(rcu_cpu_kthread_loops); +- local_irq_disable(); +- work = *workp; +- *workp = 0; +- local_irq_enable(); +- if (work) +- rcu_kthread_do_work(); +- 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 +@@ -1339,26 +1238,12 @@ 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_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_cpu_has_work, cpu) = 0; +- BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec)); + rcu_for_each_leaf_node(rcu_state_p, rnp) + (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp); + } +@@ -1381,11 +1266,6 @@ 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; +-- +2.36.1 + |