linux-kernel - [RFC PATCH v3 07/10] sched/fair: Prepare task_change_group

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Message-ID: <20240711130004.2157737-8-vschneid@redhat.com>
Date: Thu, 11 Jul 2024 15:00:01 +0200
From: Valentin Schneider <vschneid@...hat.com>
To: linux-kernel@...r.kernel.org,
	rcu@...r.kernel.org
Cc: Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Phil Auld <pauld@...hat.com>,
	Clark Williams <williams@...hat.com>,
	Tomas Glozar <tglozar@...hat.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Arnd Bergmann <arnd@...db.de>,
	Guo Ren <guoren@...nel.org>,
	Palmer Dabbelt <palmer@...osinc.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Jens Axboe <axboe@...nel.dk>
Subject: [RFC PATCH v3 07/10] sched/fair: Prepare task_change_group_fair() for per-task throttling

Later commits will change CFS bandwidth control throttling from a
per-cfs_rq basis to a per-task basis. This means special care needs to be
taken around any transition a task can have into and out of a cfs_rq.

To ease reviewing, the transitions are patched with dummy-helpers that are
implemented later on.

Add helpers to task_change_group_fair() to cover CPU cgroup
migration. If changing to a throttled taskgroup/cfs_rq, the task needs to
be throttled. Conversely, if the task is already throttled but changing to
a taskgroup/cfs_rq that still has some runtime, the task must be unthrottled.

Signed-off-by: Valentin Schneider <vschneid@...hat.com>
---
 kernel/sched/fair.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index acac0829c71f3..ec4cf7308a586 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12935,6 +12935,14 @@ static void task_change_group_fair(struct task_struct *p)
 #endif
 	set_task_rq(p, task_cpu(p));
 	attach_task_cfs_rq(p);
+
+	if (!cfs_bandwidth_used())
+		return;
+
+	if (task_needs_throttling(p))
+		task_throttle_setup(p);
+	else
+		task_throttle_cancel(p);
 }
 
 void free_fair_sched_group(struct task_group *tg)
-- 
2.43.0