linux-kernel - [PATCH] sched/core: add unlikely in group_has

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Message-Id: <20200730135423.232776-1-arch0.zheng@gmail.com>
Date:   Thu, 30 Jul 2020 21:54:23 +0800
From:   Qi Zheng <arch0.zheng@...il.com>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de
Cc:     linux-kernel@...r.kernel.org, Qi Zheng <arch0.zheng@...il.com>
Subject: [PATCH] sched/core: add unlikely in group_has_capacity()

1. The group_has_capacity() function is only called in
   group_classify().
2. Before calling the group_has_capacity() function,
   group_is_overloaded() will first judge the following
   formula, if it holds, the group_classify() will directly
   return the group_overloaded.

	(sgs->group_capacity * imbalance_pct) <
                        (sgs->group_runnable * 100)

Therefore, when the group_has_capacity() is called, the
probability that the above formalu holds is very small. Hint
compilers about that.

Signed-off-by: Qi Zheng <arch0.zheng@...il.com>
---
 kernel/sched/fair.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2ba8f230feb9..9074fd5e23b2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8234,8 +8234,8 @@ group_has_capacity(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
 	if (sgs->sum_nr_running < sgs->group_weight)
 		return true;
 
-	if ((sgs->group_capacity * imbalance_pct) <
-			(sgs->group_runnable * 100))
+	if (unlikely((sgs->group_capacity * imbalance_pct) <
+			(sgs->group_runnable * 100)))
 		return false;
 
 	if ((sgs->group_capacity * 100) >
-- 
2.25.1