From 2bd7ccf52392fe5700adb4a2555d8beddd96efa0 Mon Sep 17 00:00:00 2001
From: Luc Ma <luc@sietium.com>
Date: Tue, 14 Jan 2025 17:44:24 +0800
Subject: [PATCH] linux: [gpu-sched]describle state transition more
 specifically

Signed-off-by: Luc Ma <luc@sietium.com>
---
 source/_drafts/kernel-sync.md  | 55 ++++++++++++++++++++++++++++++++--
 source/_posts/lnx/gpu-sched.md |  4 +--
 2 files changed, 54 insertions(+), 5 deletions(-)

diff --git a/source/_drafts/kernel-sync.md b/source/_drafts/kernel-sync.md
index 0369d6089..e994dc07a 100644
--- a/source/_drafts/kernel-sync.md
+++ b/source/_drafts/kernel-sync.md
@@ -13,11 +13,60 @@ categories: linux
 
 信号量的实现基于一个变量，根据这个变量的取值范围可以把信号量分为
 
-- binary semaphore (0/1)
-- normal semaphore (non-negative integer)
+- binary semaphore (= 1, mutex)
+- normal semaphore (> 1, counting semaphore)
 
 信号量的操作叫 **Acquire** 和 **Release**, 对应的实现是 `void down(struct semaphore *)` 和 `void up(struct semaphore *)`
 
+- down
+
+```c
+static inline int __sched ___down_common(struct semaphore *sem, long state,
+								long timeout)
+{
+	struct semaphore_waiter waiter;
+
+	list_add_tail(&waiter.list, &sem->wait_list);
+	waiter.task = current;
+	waiter.up = false;
+
+	for (;;) {
+		if (signal_pending_state(state, current))
+			goto interrupted;
+		if (unlikely(timeout <= 0))
+			goto timed_out;
+		__set_current_state(state);
+		raw_spin_unlock_irq(&sem->lock);
+		timeout = schedule_timeout(timeout);
+		raw_spin_lock_irq(&sem->lock);
+		if (waiter.up)
+			return 0;
+	}
+
+ timed_out:
+	list_del(&waiter.list);
+	return -ETIME;
+
+ interrupted:
+	list_del(&waiter.list);
+	return -EINTR;
+}
+```
+
+- up
+
+```c
+static noinline void __sched __up(struct semaphore *sem)
+{
+	struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list,
+						struct semaphore_waiter, list);
+	list_del(&waiter->list);
+	waiter->up = true;
+	wake_up_process(waiter->task);
+}
+```
+
 # References
 
-- [Synchronization primitives in Linux kernel](https://0xax.gitbooks.io/linux-insides/content/SyncPrim/)
\ No newline at end of file
+- [Synchronization primitives in Linux kernel](https://0xax.gitbooks.io/linux-insides/content/SyncPrim/)
+- [https://yarchive.net/comp/linux/semaphores.html](https://yarchive.net/comp/linux/semaphores.html)
diff --git a/source/_posts/lnx/gpu-sched.md b/source/_posts/lnx/gpu-sched.md
index a208faef5..75efb13e0 100644
--- a/source/_posts/lnx/gpu-sched.md
+++ b/source/_posts/lnx/gpu-sched.md
@@ -19,11 +19,11 @@ stateDiagram-v2
     P: parked
     I: idle
 
-    R --> S: Wait for Sth
+    R --> S: schedule_timeout()
     R --> D: Wait for Disk I/O
     R --> T: SIGTSTP
     R --> t: gdb/strace
-    S --> R: Sth Available
+    S --> R: wake_up_process()
     D --> R: I/O Completed
     T --> R: SIGCONT
     T --> t: gdb/strace