On Tue, Dec 14, 2021 at 07:46:25PM -0800, Peter Oskolkov wrote:

quoted

On Tue, Dec 14, 2021 at 12:55 PM Peter Zijlstra [off-list ref] wrote:

quoted

Hi,

This is actually tested code; but still missing the SMP wake-to-idle machinery.
I still need to think about that.

Thanks, Peter!

At a first glance, your main patch does not look much smaller than
mine, and I thought the whole point of re-doing it was to throw away
extra features and make things smaller/simpler...

Well, simpler was the goal. I didn't really focus on size much. It isn't
really big to begin with.

But yes, it has 5 hooks now, 3 syscalls and lots of comments and all
that under 900 lines, not bad I'd say.

Also I think you wanted something like this? I'm not sure of the LAZY
name, but I can't seem to come up with anything saner atm.


---

--- a/include/linux/sched.h
+++ b/include/linux/sched.h

@@ -1297,6 +1297,7 @@ struct task_struct {
 
 #ifdef CONFIG_UMCG
 	/* setup by sys_umcg_ctrl() */
+	u32			umcg_flags;
 	clockid_t		umcg_clock;
 	struct umcg_task __user	*umcg_task;
 
--- a/include/uapi/linux/umcg.h
+++ b/include/uapi/linux/umcg.h

@@ -133,11 +133,13 @@ struct umcg_task {
  * @UMCG_CTL_REGISTER:   register the current task as a UMCG task
  * @UMCG_CTL_UNREGISTER: unregister the current task as a UMCG task
  * @UMCG_CTL_WORKER:     register the current task as a UMCG worker
+ * @UMCG_CTL_LAZY:	 don't wake server on runnable enqueue
  */
 enum umcg_ctl_flag {
 	UMCG_CTL_REGISTER	= 0x00001,
 	UMCG_CTL_UNREGISTER	= 0x00002,
 	UMCG_CTL_WORKER		= 0x10000,
+	UMCG_CTL_LAZY		= 0x20000,
 };
 
 #endif /* _UAPI_LINUX_UMCG_H */
--- a/kernel/sched/umcg.c
+++ b/kernel/sched/umcg.c

@@ -416,6 +416,27 @@ static int umcg_enqueue_runnable(struct
 }
 
 /*
+ * Enqueue tsk to it's server's runnable list and wake the server for pickup if
+ * so desired. Notable LAZY workers will not wake the server and rely on the
+ * server to do pickup whenever it naturally runs next.
+ *
+ * Returns:
+ * 0:	success
+ * -EFAULT
+ */
+static int umcg_enqueue_and_wake(struct task_struct *tsk, bool force)
+{
+	int ret = umcg_enqueue_runnable(tsk);
+	if (ret)
+		return ret;
+
+	if (force || !(tsk->umcg_flags & UMCG_CTL_LAZY))
+		ret = umcg_wake_server(tsk);
+
+	return ret;
+}