linux-kernel - [PATCH] sched: optimize __cond_resched

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Date:   Tue, 21 Dec 2021 15:23:16 +0800
From:   xuhaifeng <xuhaifeng@...o.com>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com
Cc:     linux-kernel@...r.kernel.org, xuhaifeng <xuhaifeng@...o.com>
Subject: [PATCH] sched: optimize __cond_resched_lock()

if the kernel is preemptible(CONFIG_PREEMPTION=y), schedule()may be
called twice, once via spin_unlock, once via preempt_schedule_common.

we can add one conditional, check TIF_NEED_RESCHED flag again,
to avoid this.

Signed-off-by: xuhaifeng <xuhaifeng@...o.com>
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 83872f95a1ea..fb011e613497 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8219,7 +8219,7 @@ int __cond_resched_lock(spinlock_t *lock)

        if (spin_needbreak(lock) || resched) {
                spin_unlock(lock);
-               if (resched)
+               if (resched && need_resched())
                        preempt_schedule_common();
                else
                        cpu_relax();
--
2.17.1

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