[PATCH 6/8] rcu/exp: Make parallel exp gp kworker per rcu node

Boqun Feng
2024-01-29T23:25:24Z

When CONFIG_RCU_EXP_KTHREAD=n, the expedited grace period per node
initialization is performed in parallel via workqueues (one work per
node).

However in CONFIG_RCU_EXP_KTHREAD=y, this per node initialization is
performed by a single kworker serializing each node initialization (one
work for all nodes).

The second part is certainly less scalable and efficient beyond a single
leaf node.

To improve this, expand this single kworker into per-node kworkers. This
new layout is eventually intended to remove the workqueues based
implementation since it will essentially now become duplicate code.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/rcu.h | 1 -
kernel/rcu/tree.c | 61 +++++++++++++++++++++++++++-------------
kernel/rcu/tree.h | 3 ++
kernel/rcu/tree_exp.h | 10 +++----
kernel/rcu/tree_plugin.h | 10 ++-----
5 files changed, 52 insertions(+), 33 deletions(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index f94f65877f2b..6beaf70d629f 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -625,7 +625,6 @@ void rcu_force_quiescent_state(void);
extern struct workqueue_struct *rcu_gp_wq;
#ifdef CONFIG_RCU_EXP_KTHREAD
extern struct kthread_worker *rcu_exp_gp_kworker;
-extern struct kthread_worker *rcu_exp_par_gp_kworker;
#else /* !CONFIG_RCU_EXP_KTHREAD */
extern struct workqueue_struct *rcu_par_gp_wq;
#endif /* CONFIG_RCU_EXP_KTHREAD */
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 657ac12f9e27..398c099d45d9 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4396,33 +4396,39 @@ rcu_boot_init_percpu_data(int cpu)

#ifdef CONFIG_RCU_EXP_KTHREAD
struct kthread_worker *rcu_exp_gp_kworker;
-struct kthread_worker *rcu_exp_par_gp_kworker;

-static void __init rcu_start_exp_gp_kworkers(void)
+static void rcu_spawn_exp_par_gp_kworker(struct rcu_node *rnp)
{
- const char *par_gp_kworker_name = "rcu_exp_par_gp_kthread_worker";
- const char *gp_kworker_name = "rcu_exp_gp_kthread_worker";
+ struct kthread_worker *kworker;
+ const char *name = "rcu_exp_par_gp_kthread_worker/%d";
struct sched_param param = { .sched_priority = kthread_prio };
+ int rnp_index = rnp - rcu_get_root();

- rcu_exp_gp_kworker = kthread_create_worker(0, gp_kworker_name);
- if (IS_ERR_OR_NULL(rcu_exp_gp_kworker)) {
- pr_err("Failed to create %s!\n", gp_kworker_name);
- rcu_exp_gp_kworker = NULL;
+ if (rnp->exp_kworker)
+ return;
+
+ kworker = kthread_create_worker(0, name, rnp_index);
+ if (IS_ERR_OR_NULL(kworker)) {
+ pr_err("Failed to create par gp kworker on %d/%d\n",
+ rnp->grplo, rnp->grphi);
return;
}
+ WRITE_ONCE(rnp->exp_kworker, kworker);
+ sched_setscheduler_nocheck(kworker->task, SCHED_FIFO, &param);
+}

- rcu_exp_par_gp_kworker = kthread_create_worker(0, par_gp_kworker_name);
- if (IS_ERR_OR_NULL(rcu_exp_par_gp_kworker)) {
- pr_err("Failed to create %s!\n", par_gp_kworker_name);
- rcu_exp_par_gp_kworker = NULL;
- kthread_destroy_worker(rcu_exp_gp_kworker);
+static void __init rcu_start_exp_gp_kworker(void)
+{
+ const char *name = "rcu_exp_gp_kthread_worker";
+ struct sched_param param = { .sched_priority = kthread_prio };
+
+ rcu_exp_gp_kworker = kthread_create_worker(0, name);
+ if (IS_ERR_OR_NULL(rcu_exp_gp_kworker)) {
+ pr_err("Failed to create %s!\n", name);
rcu_exp_gp_kworker = NULL;
return;
}
-
sched_setscheduler_nocheck(rcu_exp_gp_kworker->task, SCHED_FIFO, &param);
- sched_setscheduler_nocheck(rcu_exp_par_gp_kworker->task, SCHED_FIFO,
- &param);
}

static inline void rcu_alloc_par_gp_wq(void)
@@ -4431,7 +4437,11 @@ static inline void rcu_alloc_par_gp_wq(void)
#else /* !CONFIG_RCU_EXP_KTHREAD */
struct workqueue_struct *rcu_par_gp_wq;

-static void __init rcu_start_exp_gp_kworkers(void)
+static void rcu_spawn_exp_par_gp_kworker(struct rcu_node *rnp)
+{
+}
+
+static void __init rcu_start_exp_gp_kworker(void)
{
}

@@ -4442,6 +4452,17 @@ static inline void rcu_alloc_par_gp_wq(void)
}
#endif /* CONFIG_RCU_EXP_KTHREAD */

+static void rcu_spawn_rnp_kthreads(struct rcu_node *rnp)
+{
+ if ((IS_ENABLED(CONFIG_RCU_EXP_KTHREAD) ||
+ IS_ENABLED(CONFIG_RCU_BOOST)) && rcu_scheduler_fully_active) {
+ mutex_lock(&rnp->kthread_mutex);
+ rcu_spawn_one_boost_kthread(rnp);
+ rcu_spawn_exp_par_gp_kworker(rnp);
+ mutex_unlock(&rnp->kthread_mutex);
+ }
+}
+
/*
* Invoked early in the CPU-online process, when pretty much all services
* are available. The incoming CPU is not present.
@@ -4490,7 +4511,7 @@ int rcutree_prepare_cpu(unsigned int cpu)
rdp->rcu_iw_gp_seq = rdp->gp_seq - 1;
trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl"));
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
- rcu_spawn_one_boost_kthread(rnp);
+ rcu_spawn_rnp_kthreads(rnp);
rcu_spawn_cpu_nocb_kthread(cpu);
WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus + 1);

@@ -4812,10 +4833,10 @@ static int __init rcu_spawn_gp_kthread(void)
* due to rcu_scheduler_fully_active.
*/
rcu_spawn_cpu_nocb_kthread(smp_processor_id());
- rcu_spawn_one_boost_kthread(rdp->mynode);
+ rcu_spawn_rnp_kthreads(rdp->mynode);
rcu_spawn_core_kthreads();
/* Create kthread worker for expedited GPs */
- rcu_start_exp_gp_kworkers();
+ rcu_start_exp_gp_kworker();
return 0;
}
early_initcall(rcu_spawn_gp_kthread);
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 13e7b0d907ab..e173808f486f 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -72,6 +72,9 @@ struct rcu_node {
/* Online CPUs for next expedited GP. */
/* Any CPU that has ever been online will */
/* have its bit set. */
+ struct kthread_worker *exp_kworker;
+ /* Workers performing per node expedited GP */
+ /* initialization. */
unsigned long cbovldmask;
/* CPUs experiencing callback overload. */
unsigned long ffmask; /* Fully functional CPUs. */
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 6123a60d9a4d..0318a8a062d5 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -432,9 +432,9 @@ static inline bool rcu_exp_worker_started(void)
return !!READ_ONCE(rcu_exp_gp_kworker);
}

-static inline bool rcu_exp_par_worker_started(void)
+static inline bool rcu_exp_par_worker_started(struct rcu_node *rnp)
{
- return !!READ_ONCE(rcu_exp_par_gp_kworker);
+ return !!READ_ONCE(rnp->exp_kworker);
}

static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
@@ -445,7 +445,7 @@ static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
* another work item on the same kthread worker can result in
* deadlock.
*/
- kthread_queue_work(rcu_exp_par_gp_kworker, &rnp->rew.rew_work);
+ kthread_queue_work(READ_ONCE(rnp->exp_kworker), &rnp->rew.rew_work);
}

static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
@@ -487,7 +487,7 @@ static inline bool rcu_exp_worker_started(void)
return !!READ_ONCE(rcu_gp_wq);
}

-static inline bool rcu_exp_par_worker_started(void)
+static inline bool rcu_exp_par_worker_started(struct rcu_node *rnp)
{
return !!READ_ONCE(rcu_par_gp_wq);
}
@@ -550,7 +550,7 @@ static void sync_rcu_exp_select_cpus(void)
rnp->exp_need_flush = false;
if (!READ_ONCE(rnp->expmask))
continue; /* Avoid early boot non-existent wq. */
- if (!rcu_exp_par_worker_started() ||
+ if (!rcu_exp_par_worker_started(rnp) ||
rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
rcu_is_last_leaf_node(rnp)) {
/* No worker started yet or last leaf, do direct call. */
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 0d307674915c..09bdd36ca9ff 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1195,14 +1195,13 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
struct sched_param sp;
struct task_struct *t;

- mutex_lock(&rnp->kthread_mutex);
- if (rnp->boost_kthread_task || !rcu_scheduler_fully_active)
- goto out;
+ if (rnp->boost_kthread_task)
+ return;

t = kthread_create(rcu_boost_kthread, (void *)rnp,
"rcub/%d", rnp_index);
if (WARN_ON_ONCE(IS_ERR(t)))
- goto out;
+ return;

raw_spin_lock_irqsave_rcu_node(rnp, flags);
rnp->boost_kthread_task = t;
@@ -1210,9 +1209,6 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
sp.sched_priority = kthread_prio;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
-
- out:
- mutex_unlock(&rnp->kthread_mutex);
}

/*
--
2.43.0