linux-kernel - [PATCH 20/30] sched: handle idle preemption for PREEMPT

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Message-Id: <20240213055554.1802415-21-ankur.a.arora@oracle.com>
Date: Mon, 12 Feb 2024 21:55:44 -0800
From: Ankur Arora <ankur.a.arora@...cle.com>
To: linux-kernel@...r.kernel.org
Cc: tglx@...utronix.de, peterz@...radead.org, torvalds@...ux-foundation.org,
        paulmck@...nel.org, akpm@...ux-foundation.org, luto@...nel.org,
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        mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org,
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        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        Ankur Arora <ankur.a.arora@...cle.com>
Subject: [PATCH 20/30] sched: handle idle preemption for PREEMPT_AUTO

When running the idle task, we always want to schedule out immediately.
Use tif_resched(NR_now) to do that.

This path should be identical across preemption models which is borne
out by comparing latency via perf bench sched pipe (5 runs):

PREEMPT_AUTO:	  4.430 usecs/op +-    0.080  ( +- 1.800% )
PREEMPT_DYNAMIC:  4.400 usecs/op +-    0.100  ( +- 2.270% )

Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Originally-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/
Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 kernel/sched/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 6596b5e0b6c8..5e3dd95efb73 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1045,6 +1045,9 @@ static resched_t resched_opt_translate(struct task_struct *curr,
 	if (!IS_ENABLED(CONFIG_PREEMPT_AUTO))
 		return NR_now;
 
+	if (is_idle_task(curr))
+		return NR_now;
+
 	return NR_lazy;
 }
 
-- 
2.31.1