sched_ext: Add rhashtable lookup for sub-schedulers

Add rhashtable-based lookup for sub-schedulers indexed by cgroup_id to
enable efficient scheduler discovery in preparation for multiple scheduler
support. The hash table allows quick lookup of the appropriate scheduler
instance when processing tasks from different cgroups.

This extends scx_link_sched() to register sub-schedulers in the hash table
and scx_unlink_sched() to remove them. A new scx_find_sub_sched() function
provides the lookup interface.

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

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 8674a5fa543772c0cbb96e413f312ec7c60f23de..9db5002a2f4bec16cd817db61685c8a43736cbc9 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -27,6 +27,16 @@ struct scx_sched __rcu *scx_root;
  */
 static LIST_HEAD(scx_sched_all);
 
+#ifdef CONFIG_EXT_SUB_SCHED
+static const struct rhashtable_params scx_sched_hash_params = {
+       .key_len                = sizeof_field(struct scx_sched, ops.sub_cgroup_id),
+       .key_offset             = offsetof(struct scx_sched, ops.sub_cgroup_id),
+       .head_offset            = offsetof(struct scx_sched, hash_node),
+};
+
+static struct rhashtable scx_sched_hash;
+#endif
+
 /*
  * During exit, a task may schedule after losing its PIDs. When disabling the
  * BPF scheduler, we need to be able to iterate tasks in every state to
@@ -287,6 +297,12 @@ static struct scx_sched *scx_next_descendant_pre(struct scx_sched *pos,
        return NULL;
 }
 
+static struct scx_sched *scx_find_sub_sched(u64 cgroup_id)
+{
+       return rhashtable_lookup(&scx_sched_hash, &cgroup_id,
+                                scx_sched_hash_params);
+}
+
 static void scx_set_task_sched(struct task_struct *p, struct scx_sched *sch)
 {
        rcu_assign_pointer(p->scx.sched, sch);
@@ -294,6 +310,7 @@ static void scx_set_task_sched(struct task_struct *p, struct scx_sched *sch)
 #else  /* CONFIG_EXT_SUB_SCHED */
 static struct scx_sched *scx_parent(struct scx_sched *sch) { return NULL; }
 static struct scx_sched *scx_next_descendant_pre(struct scx_sched *pos, struct scx_sched *root) { return pos ? NULL : root; }
+static struct scx_sched *scx_find_sub_sched(u64 cgroup_id) { return NULL; }
 static void scx_set_task_sched(struct task_struct *p, struct scx_sched *sch) {}
 #endif /* CONFIG_EXT_SUB_SCHED */
 
@@ -4830,26 +4847,41 @@ static void refresh_watchdog(void)
                cancel_delayed_work_sync(&scx_watchdog_work);
 }
 
-static void scx_link_sched(struct scx_sched *sch)
+static s32 scx_link_sched(struct scx_sched *sch)
 {
        scoped_guard(raw_spinlock_irq, &scx_sched_lock) {
 #ifdef CONFIG_EXT_SUB_SCHED
                struct scx_sched *parent = scx_parent(sch);
-               if (parent)
+               s32 ret;
+
+               if (parent) {
+                       ret = rhashtable_lookup_insert_fast(&scx_sched_hash,
+                                       &sch->hash_node, scx_sched_hash_params);
+                       if (ret) {
+                               scx_error(sch, "failed to insert into scx_sched_hash (%d)", ret);
+                               return ret;
+                       }
+
                        list_add_tail(&sch->sibling, &parent->children);
+               }
 #endif /* CONFIG_EXT_SUB_SCHED */
+
                list_add_tail_rcu(&sch->all, &scx_sched_all);
        }
 
        refresh_watchdog();
+       return 0;
 }
 
 static void scx_unlink_sched(struct scx_sched *sch)
 {
        scoped_guard(raw_spinlock_irq, &scx_sched_lock) {
 #ifdef CONFIG_EXT_SUB_SCHED
-               if (scx_parent(sch))
+               if (scx_parent(sch)) {
+                       rhashtable_remove_fast(&scx_sched_hash, &sch->hash_node,
+                                              scx_sched_hash_params);
                        list_del_init(&sch->sibling);
+               }
 #endif /* CONFIG_EXT_SUB_SCHED */
                list_del_rcu(&sch->all);
        }
@@ -5906,7 +5938,9 @@ static void scx_root_enable_workfn(struct kthread_work *work)
         */
        rcu_assign_pointer(scx_root, sch);
 
-       scx_link_sched(sch);
+       ret = scx_link_sched(sch);
+       if (ret)
+               goto err_disable;
 
        scx_idle_enable(ops);
 
@@ -6171,7 +6205,9 @@ static void scx_sub_enable_workfn(struct kthread_work *work)
                goto out_put_cgrp;
        }
 
-       scx_link_sched(sch);
+       ret = scx_link_sched(sch);
+       if (ret)
+               goto err_disable;
 
        if (sch->level >= SCX_SUB_MAX_DEPTH) {
                scx_error(sch, "max nesting depth %d violated",
@@ -6999,6 +7035,10 @@ void __init init_sched_ext_class(void)
        register_sysrq_key('S', &sysrq_sched_ext_reset_op);
        register_sysrq_key('D', &sysrq_sched_ext_dump_op);
        INIT_DELAYED_WORK(&scx_watchdog_work, scx_watchdog_workfn);
+
+#ifdef CONFIG_EXT_SUB_SCHED
+       BUG_ON(rhashtable_init(&scx_sched_hash, &scx_sched_hash_params));
+#endif /* CONFIG_EXT_SUB_SCHED */
 }
 
 

diff --git a/kernel/sched/ext_internal.h b/kernel/sched/ext_internal.h
index aac051e27f7f5cf2a0412e5a469f9d8f72ebf3b6..4cb97093b87270e9565e6ff30339638e6bc58f7a 100644 (file)
--- a/kernel/sched/ext_internal.h
+++ b/kernel/sched/ext_internal.h
@@ -1014,6 +1014,8 @@ struct scx_sched {
        struct list_head        all;
 
 #ifdef CONFIG_EXT_SUB_SCHED
+       struct rhash_head       hash_node;
+
        struct list_head        children;
        struct list_head        sibling;
        struct cgroup           *cgrp;