sched/hrtimer: add option for list-based hrtimer management

Add support for managing hrtimers using a simple list. This approach
  is more memory-efficient, as list nodes use less memory, and it is
  preferable to an RB-tree when the number of hrtimers is relatively small.

Signed-off-by: Chengdong Wang <wangchengdong@lixiang.com>

include/nuttx/hrtimer.h

@@ -31,6 +31,7 @@
 #include <nuttx/clock.h>
 #include <nuttx/compiler.h>
 #include <nuttx/spinlock.h>
+#include <nuttx/list.h>
 
 #include <stdint.h>
 #include <sys/tree.h>
@@ -68,7 +69,11 @@ typedef CODE uint64_t (*hrtimer_entry_t)(FAR const struct hrtimer_s *hrtimer,
 
 typedef struct hrtimer_node_s
 {
+#ifdef CONFIG_HRTIMER_TREE
   RB_ENTRY(hrtimer_node_s) entry;  /* RB-tree linkage */
+#else
+  struct list_node entry;  /* List linkage */
+#endif
 } hrtimer_node_t;
 
 /* High-resolution timer object

sched/Kconfig

@@ -2067,3 +2067,28 @@ config HRTIMER
 	default n
 	---help---
 		Enable to support high resolution timer
+
+if HRTIMER
+
+choice
+    prompt "HRTimer management data structure type"
+    default HRTIMER_TREE
+
+config HRTIMER_LIST
+    bool "List-based timer management"
+    help
+        Use a simple list to manage timers. This method is
+        suitable for systems with a small number of timers.
+        It is more memory-efficient but may become slower
+        as the number of timers increases.
+
+config HRTIMER_TREE
+    bool "RB-tree-based timer management"
+    help
+        Use a red-black tree to manage timers. This method
+        provides better performance for systems with many
+        timers, at the cost of slightly higher memory usage.
+
+endchoice
+
+endif # HRTIMER

sched/hrtimer/hrtimer.h

@@ -44,7 +44,9 @@
  * being the left-most (minimum) node in the tree.
  */
 
+#ifdef CONFIG_HRTIMER_TREE
 RB_HEAD(hrtimer_tree_s, hrtimer_node_s);
+#endif
 
 /****************************************************************************
  * Public Data
@@ -54,9 +56,15 @@ RB_HEAD(hrtimer_tree_s, hrtimer_node_s);
 
 extern spinlock_t g_hrtimer_spinlock;
 
+#ifdef CONFIG_HRTIMER_TREE
 /* Red-Black tree containing all active high-resolution timers */
 
 extern struct hrtimer_tree_s g_hrtimer_tree;
+#else
+/* List containing all active high-resolution timers */
+
+extern struct list_node g_hrtimer_list;
+#endif
 
 /* Array of pointers to currently running high-resolution timers
  * for each CPU in SMP configurations. Index corresponds to CPU ID.
@@ -165,6 +173,7 @@ int hrtimer_starttimer(uint64_t ns)
  *   >=0 if a expires after b
  ****************************************************************************/
 
+#ifdef CONFIG_HRTIMER_TREE
 static inline_function
 int hrtimer_compare(FAR const hrtimer_node_t *a,
                     FAR const hrtimer_node_t *b)
@@ -174,6 +183,7 @@ int hrtimer_compare(FAR const hrtimer_node_t *a,
 
   return clock_compare(atimer->expired, btimer->expired) ? -1 : 1;
 }
+#endif
 
 /****************************************************************************
  * Red-Black Tree Prototype for high-resolution timers
@@ -184,7 +194,9 @@ int hrtimer_compare(FAR const hrtimer_node_t *a,
  *   operations based on timer expiration time.
  ****************************************************************************/
 
+#ifdef CONFIG_HRTIMER_TREE
 RB_PROTOTYPE(hrtimer_tree_s, hrtimer_node_s, entry, hrtimer_compare);
+#endif
 
 /****************************************************************************
  * Name: hrtimer_is_armed
@@ -210,7 +222,11 @@ static inline_function bool hrtimer_is_armed(FAR hrtimer_t *hrtimer)
 
 static inline_function void hrtimer_remove(FAR hrtimer_t *hrtimer)
 {
+#ifdef CONFIG_HRTIMER_TREE
   RB_REMOVE(hrtimer_tree_s, &g_hrtimer_tree, &hrtimer->node);
+#else
+  list_delete_fast(&hrtimer->node.entry);
+#endif
 
   /* Explicitly clear parent to mark the timer as unarmed */
 
@@ -226,7 +242,24 @@ static inline_function void hrtimer_remove(FAR hrtimer_t *hrtimer)
 
 static inline_function void hrtimer_insert(FAR hrtimer_t *hrtimer)
 {
+#ifdef CONFIG_HRTIMER_TREE
   RB_INSERT(hrtimer_tree_s, &g_hrtimer_tree, &hrtimer->node);
+#else
+  FAR hrtimer_t *curr;
+  uint64_t expired = hrtimer->expired;
+
+  list_for_every_entry(&g_hrtimer_list, curr, hrtimer_t, node.entry)
+    {
+      /* Until curr->expired has not timed out relative to expired */
+
+      if (!clock_compare(curr->expired, expired))
+        {
+          break;
+        }
+    }
+
+  list_add_before(&curr->node.entry, &hrtimer->node.entry);
+#endif
 }
 
 /****************************************************************************
@@ -241,7 +274,11 @@ static inline_function void hrtimer_insert(FAR hrtimer_t *hrtimer)
 
 static inline_function FAR hrtimer_t *hrtimer_get_first(void)
 {
+#ifdef CONFIG_HRTIMER_TREE
   return (FAR hrtimer_t *)RB_MIN(hrtimer_tree_s, &g_hrtimer_tree);
+#else
+  return list_first_entry(&g_hrtimer_list, FAR hrtimer_t, node.entry);
+#endif
 }
 
 /****************************************************************************
@@ -265,7 +302,11 @@ static inline_function FAR hrtimer_t *hrtimer_get_first(void)
 
 static inline_function bool hrtimer_is_first(FAR hrtimer_t *hrtimer)
 {
+#ifdef CONFIG_HRTIMER_TREE
   return RB_LEFT(&hrtimer->node, entry) == NULL;
+#else
+  return hrtimer == list_first_entry(&g_hrtimer_list, hrtimer_t, node.entry);
+#endif
 }
 
 #endif /* CONFIG_HRTIMER */

sched/hrtimer/hrtimer_initialize.c

@@ -57,7 +57,11 @@ spinlock_t g_hrtimer_spinlock = SP_UNLOCKED;
  * The tree is ordered by absolute expiration time.
  */
 
+#ifdef CONFIG_HRTIMER_TREE
 struct hrtimer_tree_s g_hrtimer_tree = RB_INITIALIZER(g_hrtimer_tree);
+#else
+struct list_node g_hrtimer_list = LIST_INITIAL_VALUE(g_hrtimer_list);
+#endif
 
 /****************************************************************************
  * Public Functions
@@ -83,4 +87,6 @@ struct hrtimer_tree_s g_hrtimer_tree = RB_INITIALIZER(g_hrtimer_tree);
  *     core (e.g., hrtimer_start(), hrtimer_cancel(), and expire paths).
  ****************************************************************************/
 
+#ifdef CONFIG_HRTIMER_TREE
 RB_GENERATE(hrtimer_tree_s, hrtimer_node_s, entry, hrtimer_compare);
+#endif