linux-kernel - [PATCH 09/17] sched/core: Add support for nohz

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Message-ID: <20251119124449.1149616-10-sshegde@linux.ibm.com>
Date: Wed, 19 Nov 2025 18:14:41 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc: sshegde@...ux.ibm.com, mingo@...hat.com, peterz@...radead.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org, tglx@...utronix.de,
        yury.norov@...il.com, maddy@...ux.ibm.com, srikar@...ux.ibm.com,
        gregkh@...uxfoundation.org, pbonzini@...hat.com, seanjc@...gle.com,
        kprateek.nayak@....com, vschneid@...hat.com, iii@...ux.ibm.com,
        huschle@...ux.ibm.com, rostedt@...dmis.org, dietmar.eggemann@....com,
        christophe.leroy@...roup.eu
Subject: [PATCH 09/17] sched/core: Add support for nohz_full CPUs

Enable tick on nohz full CPU when it is marked as paravirt.
If there in no CFS/RT running there, disable the tick to save the power.

In addition to this, arch specific code which enables the paravirt CPU
should call, tick_nohz_dep_set_cpu with TICK_DEP_BIT_SCHED for moving
the task out of nohz_full CPU fast.

Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
---
 kernel/sched/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 90fc04d84b74..73d1d49a3c72 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1336,6 +1336,10 @@ bool sched_can_stop_tick(struct rq *rq)
 {
 	int fifo_nr_running;
 
+	/* Keep the tick running until both RT and CFS are pushed out*/
+	if (cpu_paravirt(rq->cpu) && (rq->rt.rt_nr_running || rq->cfs.h_nr_queued))
+		return false;
+
 	/* Deadline tasks, even if single, need the tick */
 	if (rq->dl.dl_nr_running)
 		return false;
-- 
2.47.3