linux-kernel - [PATCH] schedule: use unlikely()

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Date:   Mon, 13 Nov 2017 14:00:45 -0500 (EST)
From:   Mikulas Patocka <mpatocka@...hat.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] schedule: use unlikely()

A small patch for schedule(), so that the code goes straght in the common
case.

Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>

---
 include/linux/blkdev.h |    2 +-
 kernel/sched/core.c    |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

Index: linux-2.6/include/linux/blkdev.h
===================================================================
--- linux-2.6.orig/include/linux/blkdev.h
+++ linux-2.6/include/linux/blkdev.h
@@ -1308,7 +1308,7 @@ static inline bool blk_needs_flush_plug(
 {
 	struct blk_plug *plug = tsk->plug;
 
-	return plug &&
+	return unlikely(plug != NULL) &&
 		(!list_empty(&plug->list) ||
 		 !list_empty(&plug->mq_list) ||
 		 !list_empty(&plug->cb_list));
Index: linux-2.6/kernel/sched/core.c
===================================================================
--- linux-2.6.orig/kernel/sched/core.c
+++ linux-2.6/kernel/sched/core.c
@@ -3405,7 +3405,7 @@ void __noreturn do_task_dead(void)
 
 static inline void sched_submit_work(struct task_struct *tsk)
 {
-	if (!tsk->state || tsk_is_pi_blocked(tsk))
+	if (!tsk->state || unlikely(tsk_is_pi_blocked(tsk)))
 		return;
 	/*
 	 * If we are going to sleep and we have plugged IO queued,