From: Willy Tarreau <w@1wt.eu>
Date: Fri, 31 Jan 2020 09:48:10 +0000 (+0100)
Subject: MINOR: task: permanently flag tasklets waking themselves up
X-Git-Tag: v2.2-dev2~52
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=bb238834da6bfe0d70a47d2d8fb0ecfe161b58a9;p=thirdparty%2Fhaproxy.git

MINOR: task: permanently flag tasklets waking themselves up

Commit a17664d829 ("MEDIUM: tasks: automatically requeue into the bulk
queue an already running tasklet") tried to inflict a penalty to
self-requeuing tasks/tasklets which correspond to those involved in
large, high-latency data transfers, for the benefit of all other
processing which requires a low latency. However, it turns out that
while it ought to do this on a case-by-case basis, basing itself on
the RUNNING flag isn't accurate because this flag doesn't leave for
tasklets, so we'd rather need a distinct flag to tag such tasklets.

This commit introduces TASK_SELF_WAKING to mark tasklets acting like
this. For now it's still set when TASK_RUNNING is present but this
will have to change. The flag is kept across wakeups.
---

diff --git a/include/proto/task.h b/include/proto/task.h
index ca963a1d36..53119b9d0d 100644
--- a/include/proto/task.h
+++ b/include/proto/task.h
@@ -245,10 +245,16 @@ static inline void tasklet_wakeup(struct tasklet *tl)
 	if (likely(tl->tid < 0)) {
 		/* this tasklet runs on the caller thread */
 		if (LIST_ISEMPTY(&tl->list)) {
-			if (tl->state & TASK_RUNNING)
+			if (tl->state & TASK_SELF_WAKING) {
 				LIST_ADDQ(&task_per_thread[tid].tasklets[TL_BULK], &tl->list);
-			else
+			}
+			else if (tl->state & TASK_RUNNING) {
+				_HA_ATOMIC_OR(&tl->state, TASK_SELF_WAKING);
+				LIST_ADDQ(&task_per_thread[tid].tasklets[TL_BULK], &tl->list);
+			}
+			else {
 				LIST_ADDQ(&task_per_thread[tid].tasklets[TL_URGENT], &tl->list);
+			}
 			_HA_ATOMIC_ADD(&tasks_run_queue, 1);
 		}
 	} else {
diff --git a/include/types/task.h b/include/types/task.h
index 5f7ae61e86..6ca97671f0 100644
--- a/include/types/task.h
+++ b/include/types/task.h
@@ -36,6 +36,7 @@
 #define TASK_QUEUED       0x0004  /* The task has been (re-)added to the run queue */
 #define TASK_SHARED_WQ    0x0008  /* The task's expiration may be updated by other
                                    * threads, must be set before first queue/wakeup */
+#define TASK_SELF_WAKING  0x0010  /* task/tasklet found waking itself */
 
 #define TASK_WOKEN_INIT   0x0100  /* woken up for initialisation purposes */
 #define TASK_WOKEN_TIMER  0x0200  /* woken up because of expired timer */
diff --git a/src/task.c b/src/task.c
index 3eaa9b4f6a..f1f36a914f 100644
--- a/src/task.c
+++ b/src/task.c
@@ -329,7 +329,7 @@ static int run_tasks_from_list(struct list *list, int max)
 
 	while (done < max && !LIST_ISEMPTY(list)) {
 		t = (struct task *)LIST_ELEM(list->n, struct tasklet *, list);
-		state = (t->state & TASK_SHARED_WQ) | TASK_RUNNING;
+		state = (t->state & (TASK_SHARED_WQ|TASK_SELF_WAKING)) | TASK_RUNNING;
 		state = _HA_ATOMIC_XCHG(&t->state, state);
 		__ha_barrier_atomic_store();
 		__tasklet_remove_from_tasklet_list((struct tasklet *)t);