linux-kernel - [PATCH RFC tip/core/rcu 11/14] EXP nohz: Add TICK_DEP_BIT

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Message-Id: <20190802151501.13069-11-paulmck@linux.ibm.com>
Date:   Fri,  2 Aug 2019 08:14:58 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        Frederic Weisbecker <frederic@...nel.org>,
        "Paul E . McKenney" <paulmck@...ux.ibm.com>
Subject: [PATCH RFC tip/core/rcu 11/14] EXP nohz: Add TICK_DEP_BIT_RCU

From: Frederic Weisbecker <frederic@...nel.org>

Indeed, kernel code is assumed to be quick enough (between two extended grace
periods) to avoid running the tick for RCU. But some long lasting kernel code
may require to tick temporarily.

You can use tick_nohz_dep_set_cpu(cpu, TICK_DEP_MASK_RCU) with the
following: @@@

[ paulmck: Enable use within rcutorture and from !NO_HZ_FULL kernels. ]
Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
---
 include/linux/tick.h     | 7 ++++++-
 kernel/time/tick-sched.c | 2 ++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/linux/tick.h b/include/linux/tick.h
index 196a0a7bfc4f..0dea6fb33a11 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -108,7 +108,8 @@ enum tick_dep_bits {
 	TICK_DEP_BIT_POSIX_TIMER	= 0,
 	TICK_DEP_BIT_PERF_EVENTS	= 1,
 	TICK_DEP_BIT_SCHED		= 2,
-	TICK_DEP_BIT_CLOCK_UNSTABLE	= 3
+	TICK_DEP_BIT_CLOCK_UNSTABLE	= 3,
+	TICK_DEP_BIT_RCU		= 4
 };
 
 #define TICK_DEP_MASK_NONE		0
@@ -116,6 +117,7 @@ enum tick_dep_bits {
 #define TICK_DEP_MASK_PERF_EVENTS	(1 << TICK_DEP_BIT_PERF_EVENTS)
 #define TICK_DEP_MASK_SCHED		(1 << TICK_DEP_BIT_SCHED)
 #define TICK_DEP_MASK_CLOCK_UNSTABLE	(1 << TICK_DEP_BIT_CLOCK_UNSTABLE)
+#define TICK_DEP_MASK_RCU		(1 << TICK_DEP_BIT_RCU)
 
 #ifdef CONFIG_NO_HZ_COMMON
 extern bool tick_nohz_enabled;
@@ -258,6 +260,9 @@ static inline bool tick_nohz_full_enabled(void) { return false; }
 static inline bool tick_nohz_full_cpu(int cpu) { return false; }
 static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) { }
 
+static inline void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit) { }
+static inline void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit) { }
+
 static inline void tick_dep_set(enum tick_dep_bits bit) { }
 static inline void tick_dep_clear(enum tick_dep_bits bit) { }
 static inline void tick_dep_set_cpu(int cpu, enum tick_dep_bits bit) { }
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index be9707f68024..5d4844d543cf 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -324,6 +324,7 @@ void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
 		preempt_enable();
 	}
 }
+EXPORT_SYMBOL_GPL(tick_nohz_dep_set_cpu);
 
 void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
 {
@@ -331,6 +332,7 @@ void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
 
 	atomic_andnot(BIT(bit), &ts->tick_dep_mask);
 }
+EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_cpu);
 
 /*
  * Set a per-task tick dependency. Posix CPU timers need this in order to elapse
-- 
2.17.1