Message-ID: <Z2Wf96x8PTNq8efH@yury-ThinkPad>
Date: Fri, 20 Dec 2024 08:48:55 -0800
From: Yury Norov <yury.norov@...il.com>
To: Andrea Righi <arighi@...dia.com>
Cc: Tejun Heo <tj@...nel.org>, David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] sched_ext: Introduce per-node idle cpumasks

On Tue, Dec 17, 2024 at 10:32:28AM +0100, Andrea Righi wrote:
> Using a single global idle mask can lead to inefficiencies and a lot of
> stress on the cache coherency protocol on large systems with multiple
> NUMA nodes, since all the CPUs can create a really intense read/write
> activity on the single global cpumask.
> 
> Therefore, split the global cpumask into multiple per-NUMA node cpumasks
> to improve scalability and performance on large systems.
> 
> The concept is that each cpumask will track only the idle CPUs within
> its corresponding NUMA node, treating CPUs in other NUMA nodes as busy.
> In this way concurrent access to the idle cpumask will be restricted
> within each NUMA node.
> 
> NOTE: with per-node idle cpumasks enabled scx_bpf_get_idle_cpu/smtmask()
> are returning the cpumask of the current NUMA node, instead of a single
> cpumask for all the CPUs.
> 
> Signed-off-by: Andrea Righi <arighi@...dia.com>
> ---
>  kernel/sched/ext.c | 281 +++++++++++++++++++++++++++++++++------------
>  1 file changed, 209 insertions(+), 72 deletions(-)
> 
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index a17abd2df4d4..d4666db4a212 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -894,6 +894,7 @@ static DEFINE_STATIC_KEY_FALSE(scx_builtin_idle_enabled);
>  #ifdef CONFIG_SMP
>  static DEFINE_STATIC_KEY_FALSE(scx_selcpu_topo_llc);
>  static DEFINE_STATIC_KEY_FALSE(scx_selcpu_topo_numa);
> +static DEFINE_STATIC_KEY_FALSE(scx_builtin_idle_per_node);
>  #endif
>  
>  static struct static_key_false scx_has_op[SCX_OPI_END] =
> @@ -937,11 +938,82 @@ static struct delayed_work scx_watchdog_work;
>  #define CL_ALIGNED_IF_ONSTACK __cacheline_aligned_in_smp
>  #endif
>  
> -static struct {
> +struct idle_cpumask {
>  	cpumask_var_t cpu;
>  	cpumask_var_t smt;
> -} idle_masks CL_ALIGNED_IF_ONSTACK;
> +};
> +
> +/*
> + * Make sure a NUMA node is in a valid range.
> + */
> +static int validate_node(int node)
> +{
> +	/* If no node is specified, return the current one */
> +	if (node == NUMA_NO_NODE)
> +		return numa_node_id();
> +
> +	/* Make sure node is in the range of possible nodes */
> +	if (node < 0 || node >= num_possible_nodes())
> +		return -EINVAL;
> +
> +	return node;
> +}

This is needed in BPF code, right? Kernel users should always provide
correct parameters.

> +/*
> + * cpumasks to track idle CPUs within each NUMA node.
> + *
> + * If SCX_OPS_BUILTIN_IDLE_PER_NODE is not specified, a single flat cpumask
> + * from node 0 is used to track all idle CPUs system-wide.
> + */
> +static struct idle_cpumask **idle_masks CL_ALIGNED_IF_ONSTACK;
> +
> +static struct cpumask *get_idle_mask_node(int node, bool smt)

Like Rasmus said in another thread, this 'get' prefix looks weird.

  > +/**
  > + * get_parity8 - get the parity of an u8 value
  
  I know it's prototypical bikeshedding, but what's with the "get_"
  prefix? Certainly the purpose of any pure function is to "get" the
  result of some computation. We don't have "get_strlen()".
  
  Please either just "parity8", or if you want to emphasize that this
  belongs in the bit-munging family, "bit_parity8".

So maybe idle_nodes(), idle_smt_nodes() and so on?

> +{
> +	if (!static_branch_maybe(CONFIG_NUMA, &scx_builtin_idle_per_node))
> +		return smt ? idle_masks[0]->smt : idle_masks[0]->cpu;
> +
> +	node = validate_node(node);
> + 	if (node < 0)
> +		return cpu_none_mask;

cpu_none_mask is a valid pointer. How should user distinguish invalid
parameter and empty nodemask? You should return -EINVAL.

Anyways...

This would make a horrid mess. Imagine I'm your user, and I'm
experimenting with this idle feature. I decided to begin with
per-node idle masks disabled and call it for example like:

        get_idle_mask_node(random(), true)

And it works! I get all my idle CPUs just well. So I'm happily build
my complex and huge codebase on top of it.

Then one day I decide to enable those fancy per-node idle masks
because you said they unload interconnect and whatever... At that
point what I want is to click a button just to collect some perf
numbers. So I do that, and I find all my codebase coredumped in some
random place... Because per-node idle masks basic functions
simply have different interface: they disallow node = random() as
parameter, while global idle mask is OK with it.

> +
> +	return smt ? idle_masks[node]->smt : idle_masks[node]->cpu;
> +}
> +
> +static struct cpumask *get_idle_cpumask_node(int node)

inline or __always_inline?

> +{
> +	return get_idle_mask_node(node, false);
> +}
> +
> +static struct cpumask *get_idle_smtmask_node(int node)
> +{
> +	return get_idle_mask_node(node, true);
> +}
> +
> +static void idle_masks_init(void)
> +{
> +	int node;
> +
> +	idle_masks = kcalloc(num_possible_nodes(), sizeof(*idle_masks), GFP_KERNEL);
> +	BUG_ON(!idle_masks);
> +
> +	for_each_node_state(node, N_POSSIBLE) {
> +		idle_masks[node] = kzalloc_node(sizeof(**idle_masks), GFP_KERNEL, node);
> +		BUG_ON(!idle_masks[node]);
> +
> +		BUG_ON(!alloc_cpumask_var_node(&idle_masks[node]->cpu, GFP_KERNEL, node));
> +		BUG_ON(!alloc_cpumask_var_node(&idle_masks[node]->smt, GFP_KERNEL, node));
> +	}
> +}
> +#else	/* !CONFIG_SMP */
> +static struct cpumask *get_idle_cpumask_node(int node)
> +{
> +	return cpu_none_mask;
> +}
>  
> +static struct cpumask *get_idle_smtmask_node(int node)
> +{
> +	return cpu_none_mask;
> +}
>  #endif	/* CONFIG_SMP */
>  
>  /* for %SCX_KICK_WAIT */
> @@ -3173,6 +3245,9 @@ bool scx_prio_less(const struct task_struct *a, const struct task_struct *b,
>  
>  static bool test_and_clear_cpu_idle(int cpu)
>  {
> +	int node = cpu_to_node(cpu);
> +	struct cpumask *idle_cpu = get_idle_cpumask_node(node);
> +
>  #ifdef CONFIG_SCHED_SMT
>  	/*
>  	 * SMT mask should be cleared whether we can claim @cpu or not. The SMT
> @@ -3181,29 +3256,34 @@ static bool test_and_clear_cpu_idle(int cpu)
>  	 */
>  	if (sched_smt_active()) {
>  		const struct cpumask *smt = cpu_smt_mask(cpu);
> +		struct cpumask *idle_smt = get_idle_smtmask_node(node);
>  
>  		/*
>  		 * If offline, @cpu is not its own sibling and
>  		 * scx_pick_idle_cpu() can get caught in an infinite loop as
> -		 * @cpu is never cleared from idle_masks.smt. Ensure that @cpu
> -		 * is eventually cleared.
> +		 * @cpu is never cleared from the idle SMT mask. Ensure that
> +		 * @cpu is eventually cleared.
> +		 *
> +		 * NOTE: Use cpumask_intersects() and cpumask_test_cpu() to
> +		 * reduce memory writes, which may help alleviate cache
> +		 * coherence pressure.
>  		 */
> -		if (cpumask_intersects(smt, idle_masks.smt))
> -			cpumask_andnot(idle_masks.smt, idle_masks.smt, smt);
> -		else if (cpumask_test_cpu(cpu, idle_masks.smt))
> -			__cpumask_clear_cpu(cpu, idle_masks.smt);
> +		if (cpumask_intersects(smt, idle_smt))
> +			cpumask_andnot(idle_smt, idle_smt, smt);
> +		else if (cpumask_test_cpu(cpu, idle_smt))
> +			__cpumask_clear_cpu(cpu, idle_smt);
>  	}
>  #endif
> -	return cpumask_test_and_clear_cpu(cpu, idle_masks.cpu);
> +	return cpumask_test_and_clear_cpu(cpu, idle_cpu);
>  }
>  
> -static s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, u64 flags)
> +static s32 scx_pick_idle_cpu_from_node(int node, const struct cpumask *cpus_allowed, u64 flags)
>  {
>  	int cpu;
>  
>  retry:
>  	if (sched_smt_active()) {
> -		cpu = cpumask_any_and_distribute(idle_masks.smt, cpus_allowed);
> +		cpu = cpumask_any_and_distribute(get_idle_smtmask_node(node), cpus_allowed);
>  		if (cpu < nr_cpu_ids)
>  			goto found;
>  
> @@ -3211,7 +3291,7 @@ static s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, u64 flags)
>  			return -EBUSY;
>  	}
>  
> -	cpu = cpumask_any_and_distribute(idle_masks.cpu, cpus_allowed);
> +	cpu = cpumask_any_and_distribute(get_idle_cpumask_node(node), cpus_allowed);
>  	if (cpu >= nr_cpu_ids)
>  		return -EBUSY;
>  
> @@ -3220,6 +3300,40 @@ static s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, u64 flags)
>  		return cpu;
>  	else
>  		goto retry;
> +
> +}
> +
> +static s32
> +scx_pick_idle_cpu_numa(const struct cpumask *cpus_allowed, s32 prev_cpu, u64 flags)

We have a sort of convention here. If you pick a cpu based on NUMA
distances, the 'numa' should be a 2nd prefix after a subsystem where
it's used. Refer for example:

        sched_numa_find_nth_cpu()
        sched_numa_hop_mask()
        for_each_numa_hop_mask()

So I'd name it scx_numa_idle_cpu()

> +{
> +	nodemask_t hop_nodes = NODE_MASK_NONE;
> +	int start_node = cpu_to_node(prev_cpu);
> +	s32 cpu = -EBUSY;
> +
> +	/*
> +	 * Traverse all online nodes in order of increasing distance,
> +	 * starting from prev_cpu's node.
> +	 */
> +	rcu_read_lock();

RCU is a leftover from for_each_numa_hop_mask(), I guess?

> +	for_each_numa_hop_node(node, start_node, hop_nodes, N_ONLINE) {
> +		cpu = scx_pick_idle_cpu_from_node(node, cpus_allowed, flags);
> +		if (cpu >= 0)
> +			break;
> +	}
> +	rcu_read_unlock();
> +
> +	return cpu;
> +}
> +
> +static s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, s32 prev_cpu, u64 flags)
> +{
> +	/*
> +	 * Only node 0 is used if per-node idle cpumasks are disabled.
> +	 */
> +	if (!static_branch_maybe(CONFIG_NUMA, &scx_builtin_idle_per_node))
> +		return scx_pick_idle_cpu_from_node(0, cpus_allowed, flags);
> +
> +	return scx_pick_idle_cpu_numa(cpus_allowed, prev_cpu, flags);
>  }
>  
>  /*
> @@ -3339,7 +3453,7 @@ static bool llc_numa_mismatch(void)
>   * CPU belongs to a single LLC domain, and that each LLC domain is entirely
>   * contained within a single NUMA node.
>   */
> -static void update_selcpu_topology(void)
> +static void update_selcpu_topology(struct sched_ext_ops *ops)
>  {
>  	bool enable_llc = false, enable_numa = false;
>  	unsigned int nr_cpus;
> @@ -3360,6 +3474,14 @@ static void update_selcpu_topology(void)
>  	if (nr_cpus > 0) {
>  		if (nr_cpus < num_online_cpus())
>  			enable_llc = true;
> +		/*
> +		 * No need to enable LLC optimization if the LLC domains are
> +		 * perfectly overlapping with the NUMA domains when per-node
> +		 * cpumasks are enabled.
> +		 */
> +		if ((ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE) &&
> +		    !llc_numa_mismatch())
> +			enable_llc = false;
>  		pr_debug("sched_ext: LLC=%*pb weight=%u\n",
>  			 cpumask_pr_args(llc_span(cpu)), llc_weight(cpu));
>  	}
> @@ -3395,6 +3517,14 @@ static void update_selcpu_topology(void)
>  		static_branch_enable_cpuslocked(&scx_selcpu_topo_numa);
>  	else
>  		static_branch_disable_cpuslocked(&scx_selcpu_topo_numa);
> +
> +	/*
> +	 * Check if we need to enable per-node cpumasks.
> +	 */
> +	if (ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE)
> +		static_branch_enable_cpuslocked(&scx_builtin_idle_per_node);
> +	else
> +		static_branch_disable_cpuslocked(&scx_builtin_idle_per_node);
>  }
>  
>  /*
> @@ -3415,6 +3545,8 @@ static void update_selcpu_topology(void)
>   * 4. Pick a CPU within the same NUMA node, if enabled:
>   *   - choose a CPU from the same NUMA node to reduce memory access latency.
>   *
> + * 5. Pick any idle CPU usable by the task.
> + *

I would make it a separate patch, or even send it independently. It
doesn't look related to the series...

>   * Step 3 and 4 are performed only if the system has, respectively, multiple
>   * LLC domains / multiple NUMA nodes (see scx_selcpu_topo_llc and
>   * scx_selcpu_topo_numa).
> @@ -3427,6 +3559,7 @@ static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
>  {
>  	const struct cpumask *llc_cpus = NULL;
>  	const struct cpumask *numa_cpus = NULL;
> +	int node = cpu_to_node(prev_cpu);
>  	s32 cpu;
>  
>  	*found = false;
> @@ -3484,9 +3617,9 @@ static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
>  		 * piled up on it even if there is an idle core elsewhere on
>  		 * the system.
>  		 */
> -		if (!cpumask_empty(idle_masks.cpu) &&
> -		    !(current->flags & PF_EXITING) &&
> -		    cpu_rq(cpu)->scx.local_dsq.nr == 0) {
> +		if (!(current->flags & PF_EXITING) &&
> +		    cpu_rq(cpu)->scx.local_dsq.nr == 0 &&
> +		    !cpumask_empty(get_idle_cpumask_node(cpu_to_node(cpu)))) {
>  			if (cpumask_test_cpu(cpu, p->cpus_ptr))
>  				goto cpu_found;
>  		}
> @@ -3500,7 +3633,7 @@ static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
>  		/*
>  		 * Keep using @prev_cpu if it's part of a fully idle core.
>  		 */
> -		if (cpumask_test_cpu(prev_cpu, idle_masks.smt) &&
> +		if (cpumask_test_cpu(prev_cpu, get_idle_smtmask_node(node)) &&
>  		    test_and_clear_cpu_idle(prev_cpu)) {
>  			cpu = prev_cpu;
>  			goto cpu_found;
> @@ -3510,7 +3643,7 @@ static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
>  		 * Search for any fully idle core in the same LLC domain.
>  		 */
>  		if (llc_cpus) {
> -			cpu = scx_pick_idle_cpu(llc_cpus, SCX_PICK_IDLE_CORE);
> +			cpu = scx_pick_idle_cpu_from_node(node, llc_cpus, SCX_PICK_IDLE_CORE);
>  			if (cpu >= 0)
>  				goto cpu_found;
>  		}
> @@ -3519,7 +3652,7 @@ static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
>  		 * Search for any fully idle core in the same NUMA node.
>  		 */
>  		if (numa_cpus) {
> -			cpu = scx_pick_idle_cpu(numa_cpus, SCX_PICK_IDLE_CORE);
> +			cpu = scx_pick_idle_cpu_from_node(node, numa_cpus, SCX_PICK_IDLE_CORE);
>  			if (cpu >= 0)
>  				goto cpu_found;
>  		}
> @@ -3527,7 +3660,7 @@ static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
>  		/*
>  		 * Search for any full idle core usable by the task.
>  		 */
> -		cpu = scx_pick_idle_cpu(p->cpus_ptr, SCX_PICK_IDLE_CORE);
> +		cpu = scx_pick_idle_cpu(p->cpus_ptr, prev_cpu, SCX_PICK_IDLE_CORE);
>  		if (cpu >= 0)
>  			goto cpu_found;
>  	}
> @@ -3544,7 +3677,7 @@ static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
>  	 * Search for any idle CPU in the same LLC domain.
>  	 */
>  	if (llc_cpus) {
> -		cpu = scx_pick_idle_cpu(llc_cpus, 0);
> +		cpu = scx_pick_idle_cpu_from_node(node, llc_cpus, 0);
>  		if (cpu >= 0)
>  			goto cpu_found;
>  	}
> @@ -3553,7 +3686,7 @@ static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
>  	 * Search for any idle CPU in the same NUMA node.
>  	 */
>  	if (numa_cpus) {
> -		cpu = scx_pick_idle_cpu(numa_cpus, 0);
> +		cpu = scx_pick_idle_cpu_from_node(node, numa_cpus, 0);
>  		if (cpu >= 0)
>  			goto cpu_found;
>  	}
> @@ -3561,7 +3694,7 @@ static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
>  	/*
>  	 * Search for any idle CPU usable by the task.
>  	 */
> -	cpu = scx_pick_idle_cpu(p->cpus_ptr, 0);
> +	cpu = scx_pick_idle_cpu(p->cpus_ptr, prev_cpu, 0);
>  	if (cpu >= 0)
>  		goto cpu_found;
>  
> @@ -3643,17 +3776,33 @@ static void set_cpus_allowed_scx(struct task_struct *p,
>  
>  static void reset_idle_masks(void)
>  {
> +	int node;
> +
> +	if (!static_branch_maybe(CONFIG_NUMA, &scx_builtin_idle_per_node)) {
> +		cpumask_copy(get_idle_cpumask_node(0), cpu_online_mask);
> +		cpumask_copy(get_idle_smtmask_node(0), cpu_online_mask);
> +		return;
> +	}
> +
>  	/*
>  	 * Consider all online cpus idle. Should converge to the actual state
>  	 * quickly.
>  	 */
> -	cpumask_copy(idle_masks.cpu, cpu_online_mask);
> -	cpumask_copy(idle_masks.smt, cpu_online_mask);
> +	for_each_node_state(node, N_POSSIBLE) {

for_each_node(node)

If the comment above is still valid, you don't need to visit every
possible node. You need to visit only N_ONLINE, or even N_CPU nodes.

This adds to the discussion in patch #1. Taking care of CPU-less nodes
is useless for the scheduler purposes. And if you don't even initialize
them, then in for_each_numa_hop_node() you should skip those nodes.

> +		const struct cpumask *node_mask = cpumask_of_node(node);
> +		struct cpumask *idle_cpu = get_idle_cpumask_node(node);
> +		struct cpumask *idle_smt = get_idle_smtmask_node(node);
> +
> +		cpumask_and(idle_cpu, cpu_online_mask, node_mask);
> +		cpumask_copy(idle_smt, idle_cpu);
> +	}
>  }
>  
>  void __scx_update_idle(struct rq *rq, bool idle)
>  {
>  	int cpu = cpu_of(rq);
> +	int node = cpu_to_node(cpu);
> +	struct cpumask *idle_cpu = get_idle_cpumask_node(node);
>  
>  	if (SCX_HAS_OP(update_idle) && !scx_rq_bypassing(rq)) {
>  		SCX_CALL_OP(SCX_KF_REST, update_idle, cpu_of(rq), idle);
> @@ -3661,27 +3810,25 @@ void __scx_update_idle(struct rq *rq, bool idle)
>  			return;
>  	}
>  
> -	if (idle)
> -		cpumask_set_cpu(cpu, idle_masks.cpu);
> -	else
> -		cpumask_clear_cpu(cpu, idle_masks.cpu);
> +	assign_cpu(cpu, idle_cpu, idle);

Can you also make it a separate preparation patch?

>  
>  #ifdef CONFIG_SCHED_SMT
>  	if (sched_smt_active()) {
>  		const struct cpumask *smt = cpu_smt_mask(cpu);
> +		struct cpumask *idle_smt = get_idle_smtmask_node(node);
>  
>  		if (idle) {
>  			/*
> -			 * idle_masks.smt handling is racy but that's fine as
> -			 * it's only for optimization and self-correcting.
> +			 * idle_smt handling is racy but that's fine as it's
> +			 * only for optimization and self-correcting.
>  			 */
>  			for_each_cpu(cpu, smt) {
> -				if (!cpumask_test_cpu(cpu, idle_masks.cpu))
> +				if (!cpumask_test_cpu(cpu, idle_cpu))
>  					return;
>  			}

So, we continue only if all smt cpus are idle. This looks like an
opencoded cpumask_subset():

                        if (!cpumask_subset(idle_cpu, smt))
                                return;

Is that true? If so, can you please again make it a small
preparation patch?

> -			cpumask_or(idle_masks.smt, idle_masks.smt, smt);
> +			cpumask_or(idle_smt, idle_smt, smt);
>  		} else {
> -			cpumask_andnot(idle_masks.smt, idle_masks.smt, smt);
> +			cpumask_andnot(idle_smt, idle_smt, smt);
>  		}
>  	}
>  #endif
> @@ -3694,7 +3841,7 @@ static void handle_hotplug(struct rq *rq, bool online)
>  	atomic_long_inc(&scx_hotplug_seq);
>  
>  	if (scx_enabled())
> -		update_selcpu_topology();
> +		update_selcpu_topology(&scx_ops);
>  
>  	if (online && SCX_HAS_OP(cpu_online))
>  		SCX_CALL_OP(SCX_KF_UNLOCKED, cpu_online, cpu);
> @@ -3729,7 +3876,10 @@ static void rq_offline_scx(struct rq *rq)
>  #else	/* CONFIG_SMP */
>  
>  static bool test_and_clear_cpu_idle(int cpu) { return false; }
> -static s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, u64 flags) { return -EBUSY; }
> +static s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, s32 prev_cpu, u64 flags)
> +{
> +	return -EBUSY;
> +}
>  static void reset_idle_masks(void) {}
>  
>  #endif	/* CONFIG_SMP */
> @@ -5579,7 +5729,7 @@ static int scx_ops_enable(struct sched_ext_ops *ops, struct bpf_link *link)
>  
>  	check_hotplug_seq(ops);
>  #ifdef CONFIG_SMP
> -	update_selcpu_topology();
> +	update_selcpu_topology(ops);
>  #endif
>  	cpus_read_unlock();
>  
> @@ -6272,8 +6422,7 @@ void __init init_sched_ext_class(void)
>  
>  	BUG_ON(rhashtable_init(&dsq_hash, &dsq_hash_params));
>  #ifdef CONFIG_SMP
> -	BUG_ON(!alloc_cpumask_var(&idle_masks.cpu, GFP_KERNEL));
> -	BUG_ON(!alloc_cpumask_var(&idle_masks.smt, GFP_KERNEL));
> +	idle_masks_init();
>  #endif
>  	scx_kick_cpus_pnt_seqs =
>  		__alloc_percpu(sizeof(scx_kick_cpus_pnt_seqs[0]) * nr_cpu_ids,
> @@ -6309,6 +6458,15 @@ void __init init_sched_ext_class(void)
>   */
>  #include <linux/btf_ids.h>
>  
> +static bool check_builtin_idle_enabled(void)
> +{
> +	if (static_branch_likely(&scx_builtin_idle_enabled))
> +		return true;
> +
> +	scx_ops_error("built-in idle tracking is disabled");
> +	return false;
> +}
> +
>  __bpf_kfunc_start_defs();
>  
>  /**
> @@ -6328,10 +6486,8 @@ __bpf_kfunc_start_defs();
>  __bpf_kfunc s32 scx_bpf_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
>  				       u64 wake_flags, bool *is_idle)
>  {
> -	if (!static_branch_likely(&scx_builtin_idle_enabled)) {
> -		scx_ops_error("built-in idle tracking is disabled");
> +	if (!check_builtin_idle_enabled())
>  		goto prev_cpu;
> -	}
>  
>  	if (!scx_kf_allowed(SCX_KF_SELECT_CPU))
>  		goto prev_cpu;
> @@ -7419,46 +7575,31 @@ __bpf_kfunc void scx_bpf_put_cpumask(const struct cpumask *cpumask)
>  
>  /**
>   * scx_bpf_get_idle_cpumask - Get a referenced kptr to the idle-tracking
> - * per-CPU cpumask.
> + * per-CPU cpumask of the current NUMA node.
>   *
>   * Returns NULL if idle tracking is not enabled, or running on a UP kernel.
>   */
>  __bpf_kfunc const struct cpumask *scx_bpf_get_idle_cpumask(void)
>  {
> -	if (!static_branch_likely(&scx_builtin_idle_enabled)) {
> -		scx_ops_error("built-in idle tracking is disabled");
> +	if (!check_builtin_idle_enabled())
>  		return cpu_none_mask;
> -	}
>  
> -#ifdef CONFIG_SMP
> -	return idle_masks.cpu;
> -#else
> -	return cpu_none_mask;
> -#endif
> +	return get_idle_cpumask_node(NUMA_NO_NODE);
>  }
>  
>  /**
>   * scx_bpf_get_idle_smtmask - Get a referenced kptr to the idle-tracking,
> - * per-physical-core cpumask. Can be used to determine if an entire physical
> - * core is free.
> + * per-physical-core cpumask of the current NUMA node. Can be used to determine
> + * if an entire physical core is free.
>   *
>   * Returns NULL if idle tracking is not enabled, or running on a UP kernel.
>   */
>  __bpf_kfunc const struct cpumask *scx_bpf_get_idle_smtmask(void)
>  {
> -	if (!static_branch_likely(&scx_builtin_idle_enabled)) {
> -		scx_ops_error("built-in idle tracking is disabled");
> +	if (!check_builtin_idle_enabled())
>  		return cpu_none_mask;
> -	}
>  
> -#ifdef CONFIG_SMP
> -	if (sched_smt_active())
> -		return idle_masks.smt;
> -	else
> -		return idle_masks.cpu;
> -#else
> -	return cpu_none_mask;
> -#endif
> +	return get_idle_smtmask_node(NUMA_NO_NODE);
>  }
>  
>  /**
> @@ -7487,10 +7628,8 @@ __bpf_kfunc void scx_bpf_put_idle_cpumask(const struct cpumask *idle_mask)
>   */
>  __bpf_kfunc bool scx_bpf_test_and_clear_cpu_idle(s32 cpu)
>  {
> -	if (!static_branch_likely(&scx_builtin_idle_enabled)) {
> -		scx_ops_error("built-in idle tracking is disabled");
> +	if (!check_builtin_idle_enabled())
>  		return false;
> -	}
>  
>  	if (ops_cpu_valid(cpu, NULL))
>  		return test_and_clear_cpu_idle(cpu);
> @@ -7520,12 +7659,10 @@ __bpf_kfunc bool scx_bpf_test_and_clear_cpu_idle(s32 cpu)
>  __bpf_kfunc s32 scx_bpf_pick_idle_cpu(const struct cpumask *cpus_allowed,
>  				      u64 flags)
>  {
> -	if (!static_branch_likely(&scx_builtin_idle_enabled)) {
> -		scx_ops_error("built-in idle tracking is disabled");
> +	if (!check_builtin_idle_enabled())
>  		return -EBUSY;
> -	}
>  
> -	return scx_pick_idle_cpu(cpus_allowed, flags);
> +	return scx_pick_idle_cpu(cpus_allowed, smp_processor_id(), flags);
>  }
>  
>  /**
> @@ -7548,7 +7685,7 @@ __bpf_kfunc s32 scx_bpf_pick_any_cpu(const struct cpumask *cpus_allowed,
>  	s32 cpu;
>  
>  	if (static_branch_likely(&scx_builtin_idle_enabled)) {
> -		cpu = scx_pick_idle_cpu(cpus_allowed, flags);
> +		cpu = scx_pick_idle_cpu(cpus_allowed, smp_processor_id(), flags);
>  		if (cpu >= 0)
>  			return cpu;
>  	}
> -- 
> 2.47.1

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