On Fri, Jul 26, 2024 at 11:56:56PM +0200, Frederic Weisbecker wrote:
> Now that kthreads have an infrastructure to handle preferred affinity
> against CPU hotplug and housekeeping cpumask, convert RCU exp workers to
> use it instead of handling all the constraints by itself.
>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Nice consolidation of troublesome code!
For this one and 17/20:
Acked-by: Paul E. McKenney <paulmck@kernel.org>
> ---
> kernel/rcu/tree.c | 105 +++++++++-------------------------------------
> 1 file changed, 19 insertions(+), 86 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index e038f4abb872..f3e40a1dea65 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -4777,6 +4777,22 @@ rcu_boot_init_percpu_data(int cpu)
> rcu_boot_init_nocb_percpu_data(rdp);
> }
>
> +static void rcu_thread_affine_rnp(struct task_struct *t, struct rcu_node *rnp)
> +{
> + cpumask_var_t affinity;
> + int cpu;
> +
> + if (!zalloc_cpumask_var(&affinity, GFP_KERNEL))
> + return;
> +
> + for_each_leaf_node_possible_cpu(rnp, cpu)
> + cpumask_set_cpu(cpu, affinity);
> +
> + kthread_affine_preferred(t, affinity);
> +
> + free_cpumask_var(affinity);
> +}
> +
> struct kthread_worker *rcu_exp_gp_kworker;
>
> static void rcu_spawn_exp_par_gp_kworker(struct rcu_node *rnp)
> @@ -4789,7 +4805,7 @@ static void rcu_spawn_exp_par_gp_kworker(struct rcu_node *rnp)
> if (rnp->exp_kworker)
> return;
>
> - kworker = kthread_run_worker(0, name, rnp_index);
> + 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);
> @@ -4799,16 +4815,9 @@ static void rcu_spawn_exp_par_gp_kworker(struct rcu_node *rnp)
>
> if (IS_ENABLED(CONFIG_RCU_EXP_KTHREAD))
> sched_setscheduler_nocheck(kworker->task, SCHED_FIFO, ¶m);
> -}
>
> -static struct task_struct *rcu_exp_par_gp_task(struct rcu_node *rnp)
> -{
> - struct kthread_worker *kworker = READ_ONCE(rnp->exp_kworker);
> -
> - if (!kworker)
> - return NULL;
> -
> - return kworker->task;
> + rcu_thread_affine_rnp(kworker->task, rnp);
> + wake_up_process(kworker->task);
> }
>
> static void __init rcu_start_exp_gp_kworker(void)
> @@ -4893,79 +4902,6 @@ int rcutree_prepare_cpu(unsigned int cpu)
> return 0;
> }
>
> -static void rcu_thread_affine_rnp(struct task_struct *t, struct rcu_node *rnp)
> -{
> - cpumask_var_t affinity;
> - int cpu;
> -
> - if (!zalloc_cpumask_var(&affinity, GFP_KERNEL))
> - return;
> -
> - for_each_leaf_node_possible_cpu(rnp, cpu)
> - cpumask_set_cpu(cpu, affinity);
> -
> - kthread_affine_preferred(t, affinity);
> -
> - free_cpumask_var(affinity);
> -}
> -
> -/*
> - * Update kthreads affinity during CPU-hotplug changes.
> - *
> - * 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
> - * held, so the value of rnp->qsmaskinit will be stable.
> - *
> - * We don't include outgoingcpu in the affinity set, use -1 if there is
> - * no outgoing CPU. If there are no CPUs left in the affinity set,
> - * this function allows the kthread to execute on any CPU.
> - *
> - * Any future concurrent calls are serialized via ->kthread_mutex.
> - */
> -static void rcutree_affinity_setting(unsigned int cpu, int outgoingcpu)
> -{
> - cpumask_var_t cm;
> - unsigned long mask;
> - struct rcu_data *rdp;
> - struct rcu_node *rnp;
> - struct task_struct *task_exp;
> -
> - rdp = per_cpu_ptr(&rcu_data, cpu);
> - rnp = rdp->mynode;
> -
> - task_exp = rcu_exp_par_gp_task(rnp);
> -
> - /*
> - * If CPU is the boot one, this task is created later from early
> - * initcall since kthreadd must be created first.
> - */
> - if (!task_exp)
> - return;
> -
> - if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
> - return;
> -
> - mutex_lock(&rnp->kthread_mutex);
> - mask = rcu_rnp_online_cpus(rnp);
> - for_each_leaf_node_possible_cpu(rnp, cpu)
> - if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
> - cpu != outgoingcpu)
> - cpumask_set_cpu(cpu, cm);
> - cpumask_and(cm, cm, housekeeping_cpumask(HK_TYPE_RCU));
> - if (cpumask_empty(cm)) {
> - cpumask_copy(cm, housekeeping_cpumask(HK_TYPE_RCU));
> - if (outgoingcpu >= 0)
> - cpumask_clear_cpu(outgoingcpu, cm);
> - }
> -
> - if (task_exp)
> - set_cpus_allowed_ptr(task_exp, cm);
> -
> - mutex_unlock(&rnp->kthread_mutex);
> -
> - free_cpumask_var(cm);
> -}
> -
> /*
> * Has the specified (known valid) CPU ever been fully online?
> */
> @@ -4994,7 +4930,6 @@ int rcutree_online_cpu(unsigned int cpu)
> if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
> return 0; /* Too early in boot for scheduler work. */
> sync_sched_exp_online_cleanup(cpu);
> - rcutree_affinity_setting(cpu, -1);
>
> // Stop-machine done, so allow nohz_full to disable tick.
> tick_dep_clear(TICK_DEP_BIT_RCU);
> @@ -5207,8 +5142,6 @@ int rcutree_offline_cpu(unsigned int cpu)
> rnp->ffmask &= ~rdp->grpmask;
> raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
>
> - rcutree_affinity_setting(cpu, cpu);
> -
> // nohz_full CPUs need the tick for stop-machine to work quickly
> tick_dep_set(TICK_DEP_BIT_RCU);
> return 0;
> --
> 2.45.2
>