linux-kernel - [PATCH V2 07/11] sched/core: Add rcu_preempt

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Date: Sun,  7 Apr 2024 17:05:54 +0800
From: Lai Jiangshan <jiangshanlai@...il.com>
To: linux-kernel@...r.kernel.org
Cc: rcu@...r.kernel.org,
	x86@...nel.org,
	Lai Jiangshan <jiangshan.ljs@...group.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <quic_neeraju@...cinc.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>
Subject: [PATCH V2 07/11] sched/core: Add rcu_preempt_switch()

From: Lai Jiangshan <jiangshan.ljs@...group.com>

When the per-cpu rcu_preempt_count is used, it has to be switched too
on context-switching.  And the instructions to switch the per-cpu
rcu_preempt_count are few, so it is inlined to avoid the overhead
in the scheduler.

Cc: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Frederic Weisbecker <frederic@...nel.org>
Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
---
 kernel/rcu/rcu.h    | 5 +++++
 kernel/sched/core.c | 2 ++
 2 files changed, 7 insertions(+)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index b17b2ed657fc..ea5ae957c687 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -668,4 +668,9 @@ int rcu_stall_notifier_call_chain(unsigned long val, void *v);
 static inline int rcu_stall_notifier_call_chain(unsigned long val, void *v) { return NOTIFY_DONE; }
 #endif // #else // #if defined(CONFIG_RCU_STALL_COMMON) && defined(CONFIG_RCU_CPU_STALL_NOTIFIER)
 
+static inline void
+rcu_preempt_switch(struct task_struct *prev, struct task_struct *next)
+{
+}
+
 #endif /* __KERNEL_RCU_H */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7019a40457a6..1d9e3c51c913 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -95,6 +95,7 @@
 #include "../workqueue_internal.h"
 #include "../../io_uring/io-wq.h"
 #include "../smpboot.h"
+#include "../rcu/rcu.h"
 
 EXPORT_TRACEPOINT_SYMBOL_GPL(ipi_send_cpu);
 EXPORT_TRACEPOINT_SYMBOL_GPL(ipi_send_cpumask);
@@ -6737,6 +6738,7 @@ static void __sched notrace __schedule(unsigned int sched_mode)
 		 */
 		++*switch_count;
 
+		rcu_preempt_switch(prev, next);
 		migrate_disable_switch(rq, prev);
 		psi_sched_switch(prev, next, !task_on_rq_queued(prev));
 
-- 
2.19.1.6.gb485710b