sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 369 insertions, 0 deletions

diff --git a/lib/interval_tree_test.c b/lib/interval_tree_test.c
new file mode 100644
index 000000000..eba2d3e28
--- /dev/null
+++ b/lib/interval_tree_test.c
@@ -0,0 +1,369 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/interval_tree.h>
+#include <linux/prandom.h>
+#include <linux/slab.h>
+#include <linux/printk.h>
+#include <asm/timex.h>
+#include <linux/bitmap.h>
+#include <linux/maple_tree.h>
+
+#define __param(type, name, init, msg)		\
+	static type name = init;		\
+	module_param(name, type, 0444);		\
+	MODULE_PARM_DESC(name, msg);
+
+__param(int, nnodes, 100, "Number of nodes in the interval tree");
+__param(int, perf_loops, 1000, "Number of iterations modifying the tree");
+
+__param(int, nsearches, 100, "Number of searches to the interval tree");
+__param(int, search_loops, 1000, "Number of iterations searching the tree");
+__param(bool, search_all, false, "Searches will iterate all nodes in the tree");
+
+__param(uint, max_endpoint, ~0, "Largest value for the interval's endpoint");
+__param(ullong, seed, 3141592653589793238ULL, "Random seed");
+
+static struct rb_root_cached root = RB_ROOT_CACHED;
+static struct interval_tree_node *nodes = NULL;
+static u32 *queries = NULL;
+
+static struct rnd_state rnd;
+
+static inline unsigned long
+search(struct rb_root_cached *root, unsigned long start, unsigned long last)
+{
+	struct interval_tree_node *node;
+	unsigned long results = 0;
+
+	for (node = interval_tree_iter_first(root, start, last); node;
+	     node = interval_tree_iter_next(node, start, last))
+		results++;
+	return results;
+}
+
+static void init(void)
+{
+	int i;
+
+	for (i = 0; i < nnodes; i++) {
+		u32 b = (prandom_u32_state(&rnd) >> 4) % max_endpoint;
+		u32 a = (prandom_u32_state(&rnd) >> 4) % b;
+
+		nodes[i].start = a;
+		nodes[i].last = b;
+	}
+
+	/*
+	 * Limit the search scope to what the user defined.
+	 * Otherwise we are merely measuring empty walks,
+	 * which is pointless.
+	 */
+	for (i = 0; i < nsearches; i++)
+		queries[i] = (prandom_u32_state(&rnd) >> 4) % max_endpoint;
+}
+
+static int basic_check(void)
+{
+	int i, j;
+	cycles_t time1, time2, time;
+
+	printk(KERN_ALERT "interval tree insert/remove");
+
+	init();
+
+	time1 = get_cycles();
+
+	for (i = 0; i < perf_loops; i++) {
+		for (j = 0; j < nnodes; j++)
+			interval_tree_insert(nodes + j, &root);
+		for (j = 0; j < nnodes; j++)
+			interval_tree_remove(nodes + j, &root);
+	}
+
+	time2 = get_cycles();
+	time = time2 - time1;
+
+	time = div_u64(time, perf_loops);
+	printk(" -> %llu cycles\n", (unsigned long long)time);
+
+	return 0;
+}
+
+static int search_check(void)
+{
+	int i, j;
+	unsigned long results;
+	cycles_t time1, time2, time;
+
+	printk(KERN_ALERT "interval tree search");
+
+	init();
+
+	for (j = 0; j < nnodes; j++)
+		interval_tree_insert(nodes + j, &root);
+
+	time1 = get_cycles();
+
+	results = 0;
+	for (i = 0; i < search_loops; i++)
+		for (j = 0; j < nsearches; j++) {
+			unsigned long start = search_all ? 0 : queries[j];
+			unsigned long last = search_all ? max_endpoint : queries[j];
+
+			results += search(&root, start, last);
+		}
+
+	time2 = get_cycles();
+	time = time2 - time1;
+
+	time = div_u64(time, search_loops);
+	results = div_u64(results, search_loops);
+	printk(" -> %llu cycles (%lu results)\n",
+	       (unsigned long long)time, results);
+
+	for (j = 0; j < nnodes; j++)
+		interval_tree_remove(nodes + j, &root);
+
+	return 0;
+}
+
+static int intersection_range_check(void)
+{
+	int i, j, k;
+	unsigned long start, last;
+	struct interval_tree_node *node;
+	unsigned long *intxn1;
+	unsigned long *intxn2;
+
+	printk(KERN_ALERT "interval tree iteration\n");
+
+	intxn1 = bitmap_alloc(nnodes, GFP_KERNEL);
+	if (!intxn1) {
+		WARN_ON_ONCE("Failed to allocate intxn1\n");
+		return -ENOMEM;
+	}
+
+	intxn2 = bitmap_alloc(nnodes, GFP_KERNEL);
+	if (!intxn2) {
+		WARN_ON_ONCE("Failed to allocate intxn2\n");
+		bitmap_free(intxn1);
+		return -ENOMEM;
+	}
+
+	for (i = 0; i < search_loops; i++) {
+		/* Initialize interval tree for each round */
+		init();
+		for (j = 0; j < nnodes; j++)
+			interval_tree_insert(nodes + j, &root);
+
+		/* Let's try nsearches different ranges */
+		for (k = 0; k < nsearches; k++) {
+			/* Try whole range once */
+			if (!k) {
+				start = 0UL;
+				last = ULONG_MAX;
+			} else {
+				last = (prandom_u32_state(&rnd) >> 4) % max_endpoint;
+				start = (prandom_u32_state(&rnd) >> 4) % last;
+			}
+
+			/* Walk nodes to mark intersection nodes */
+			bitmap_zero(intxn1, nnodes);
+			for (j = 0; j < nnodes; j++) {
+				node = nodes + j;
+
+				if (start <= node->last && last >= node->start)
+					bitmap_set(intxn1, j, 1);
+			}
+
+			/* Iterate tree to clear intersection nodes */
+			bitmap_zero(intxn2, nnodes);
+			for (node = interval_tree_iter_first(&root, start, last); node;
+			     node = interval_tree_iter_next(node, start, last))
+				bitmap_set(intxn2, node - nodes, 1);
+
+			WARN_ON_ONCE(!bitmap_equal(intxn1, intxn2, nnodes));
+		}
+
+		for (j = 0; j < nnodes; j++)
+			interval_tree_remove(nodes + j, &root);
+	}
+
+	bitmap_free(intxn1);
+	bitmap_free(intxn2);
+	return 0;
+}
+
+#ifdef CONFIG_INTERVAL_TREE_SPAN_ITER
+/*
+ * Helper function to get span of current position from maple tree point of
+ * view.
+ */
+static void mas_cur_span(struct ma_state *mas, struct interval_tree_span_iter *state)
+{
+	unsigned long cur_start;
+	unsigned long cur_last;
+	int is_hole;
+
+	if (mas->status == ma_overflow)
+		return;
+
+	/* walk to current position */
+	state->is_hole = mas_walk(mas) ? 0 : 1;
+
+	cur_start = mas->index < state->first_index ?
+			state->first_index : mas->index;
+
+	/* whether we have followers */
+	do {
+
+		cur_last = mas->last > state->last_index ?
+				state->last_index : mas->last;
+
+		is_hole = mas_next_range(mas, state->last_index) ? 0 : 1;
+
+	} while (mas->status != ma_overflow && is_hole == state->is_hole);
+
+	if (state->is_hole) {
+		state->start_hole = cur_start;
+		state->last_hole = cur_last;
+	} else {
+		state->start_used = cur_start;
+		state->last_used = cur_last;
+	}
+
+	/* advance position for next round */
+	if (mas->status != ma_overflow)
+		mas_set(mas, cur_last + 1);
+}
+
+static int span_iteration_check(void)
+{
+	int i, j, k;
+	unsigned long start, last;
+	struct interval_tree_span_iter span, mas_span;
+
+	DEFINE_MTREE(tree);
+
+	MA_STATE(mas, &tree, 0, 0);
+
+	printk(KERN_ALERT "interval tree span iteration\n");
+
+	for (i = 0; i < search_loops; i++) {
+		/* Initialize interval tree for each round */
+		init();
+		for (j = 0; j < nnodes; j++)
+			interval_tree_insert(nodes + j, &root);
+
+		/* Put all the range into maple tree */
+		mt_init_flags(&tree, MT_FLAGS_ALLOC_RANGE);
+		mt_set_in_rcu(&tree);
+
+		for (j = 0; j < nnodes; j++)
+			WARN_ON_ONCE(mtree_store_range(&tree, nodes[j].start,
+					nodes[j].last, nodes + j, GFP_KERNEL));
+
+		/* Let's try nsearches different ranges */
+		for (k = 0; k < nsearches; k++) {
+			/* Try whole range once */
+			if (!k) {
+				start = 0UL;
+				last = ULONG_MAX;
+			} else {
+				last = (prandom_u32_state(&rnd) >> 4) % max_endpoint;
+				start = (prandom_u32_state(&rnd) >> 4) % last;
+			}
+
+			mas_span.first_index = start;
+			mas_span.last_index = last;
+			mas_span.is_hole = -1;
+			mas_set(&mas, start);
+
+			interval_tree_for_each_span(&span, &root, start, last) {
+				mas_cur_span(&mas, &mas_span);
+
+				WARN_ON_ONCE(span.is_hole != mas_span.is_hole);
+
+				if (span.is_hole) {
+					WARN_ON_ONCE(span.start_hole != mas_span.start_hole);
+					WARN_ON_ONCE(span.last_hole != mas_span.last_hole);
+				} else {
+					WARN_ON_ONCE(span.start_used != mas_span.start_used);
+					WARN_ON_ONCE(span.last_used != mas_span.last_used);
+				}
+			}
+
+		}
+
+		WARN_ON_ONCE(mas.status != ma_overflow);
+
+		/* Cleanup maple tree for each round */
+		mtree_destroy(&tree);
+		/* Cleanup interval tree for each round */
+		for (j = 0; j < nnodes; j++)
+			interval_tree_remove(nodes + j, &root);
+	}
+	return 0;
+}
+#else
+static inline int span_iteration_check(void) {return 0; }
+#endif
+
+static int interval_tree_test_init(void)
+{
+	if (nnodes <= 0) {
+		pr_warn("nnodes must be positive\n");
+		return -EINVAL;
+	}
+	if (nsearches <= 0) {
+		pr_warn("nsearches must be positive\n");
+		return -EINVAL;
+	}
+	if (perf_loops <= 0) {
+		pr_warn("perf_loops must be positive\n");
+		return -EINVAL;
+	}
+	if (search_loops <= 0) {
+		pr_warn("search_loops must be positive\n");
+		return -EINVAL;
+	}
+	if (max_endpoint < 2) {
+		pr_warn("max_endpoint must be at least 2\n");
+		return -EINVAL;
+	}
+
+	nodes = kmalloc_objs(struct interval_tree_node, nnodes);
+	if (!nodes)
+		return -ENOMEM;
+
+	queries = kmalloc_array(nsearches, sizeof(int), GFP_KERNEL);
+	if (!queries) {
+		kfree(nodes);
+		return -ENOMEM;
+	}
+
+	prandom_seed_state(&rnd, seed);
+
+	basic_check();
+	search_check();
+	intersection_range_check();
+	span_iteration_check();
+
+	kfree(queries);
+	kfree(nodes);
+
+	return -EAGAIN; /* Fail will directly unload the module */
+}
+
+static void interval_tree_test_exit(void)
+{
+	printk(KERN_ALERT "test exit\n");
+}
+
+module_init(interval_tree_test_init)
+module_exit(interval_tree_test_exit)
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Michel Lespinasse");
+MODULE_DESCRIPTION("Interval Tree test");