From: Keith Packard <keithp@keithp.com>
Date: Sun, 13 Nov 2022 06:47:00 +0000 (-0800)
Subject: altos: Avoid modulus in task queue on parts without idiv
X-Git-Tag: 1.9.13~1^2~26^2~8
X-Git-Url: https://git.gag.com/?p=fw%2Faltos;a=commitdiff_plain;h=8c0a7dfa4ba4b46dabce0ac7daecf0edd5fb6b62

altos: Avoid modulus in task queue on parts without idiv

Cortex-M0 parts don't have a hardware divide, so doing a modulus
to compute task hash indexes is super slow. Avoid that by making the sleep
queue a power of two.

Signed-off-by: Keith Packard <keithp@keithp.com>
---

diff --git a/src/kernel/ao_task.c b/src/kernel/ao_task.c
index dd278bde..b5045416 100644
--- a/src/kernel/ao_task.c
+++ b/src/kernel/ao_task.c
@@ -57,7 +57,17 @@ static inline void ao_check_stack(void) {
 #endif
 
 #ifndef SLEEP_HASH_SIZE
+#ifdef __ARM_FEATURE_IDIV__
 #define SLEEP_HASH_SIZE	17
+#else
+#define SLEEP_HASH_SIZE 16
+#endif
+#endif
+
+#if SLEEP_HASH_SIZE & (SLEEP_HASH_SIZE - 1)
+#define SLEEP_HASH_SHIFT 0
+#else
+#define SLEEP_HASH_SHIFT 2
 #endif
 
 static struct ao_list	run_queue;
@@ -75,7 +85,7 @@ _ao_task_to_run_queue(struct ao_task *task)
 static struct ao_list *
 ao_task_sleep_queue(void *wchan)
 {
-	return &ao_sleep_queue[(uintptr_t) wchan % SLEEP_HASH_SIZE];
+	return &ao_sleep_queue[(((uintptr_t) wchan) >> SLEEP_HASH_SHIFT) % SLEEP_HASH_SIZE];
 }
 
 static void