From: Willy Tarreau <w@1wt.eu>
Date: Thu, 25 Feb 2021 06:19:45 +0000 (+0100)
Subject: MINOR: task: don't decrement then increment the local run queue
X-Git-Tag: v2.4-dev10~43
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=c9afbb10f5430ffce9aacd020ef46522d7e675cc;p=thirdparty%2Fhaproxy.git

MINOR: task: don't decrement then increment the local run queue

Now we don't need to decrement rq_total when we pick a tack in the tree
to immediately increment it again after installing it into the local
list. Instead, we simply add to the local queue count the number of
globally picked tasks. Avoiding this shows ~0.5% performance gains at
1Mreq/s (2M task switches/s).
---

diff --git a/src/task.c b/src/task.c
index df6fbd5c0f..b2054320e9 100644
--- a/src/task.c
+++ b/src/task.c
@@ -701,7 +701,6 @@ void process_runnable_tasks()
 		if (likely(!grq || (lrq && (int)(lrq->key - grq->key) <= 0))) {
 			t = eb32sc_entry(lrq, struct task, rq);
 			lrq = eb32sc_next(lrq, tid_bit);
-			_HA_ATOMIC_SUB(&sched->rq_total, 1);
 			eb32sc_delete(&t->rq);
 			lpicked++;
 		}
@@ -739,7 +738,8 @@ void process_runnable_tasks()
 	if (lpicked + gpicked) {
 		tt->tl_class_mask |= 1 << TL_NORMAL;
 		_HA_ATOMIC_ADD(&tt->tasks_in_list, lpicked + gpicked);
-		_HA_ATOMIC_ADD(&tt->rq_total, lpicked + gpicked);
+		if (gpicked)
+			_HA_ATOMIC_ADD(&tt->rq_total, gpicked);
 		activity[tid].tasksw += lpicked + gpicked;
 	}