[PATCH v3 0/5] Implement call_rcu_lazy() and miscellaneous fixes

[PATCH v3 0/5] Implement call_rcu_lazy() and miscellaneous fixes

[Joel Fernandes (Google)]

Hello!

Please find the next improved version of call_rcu_lazy() attached.  The main
difference between the previous versions is that:
- In v2 rcu_barrier is fixed to not hang (I found this to be due to a missing
  GP thread wakeup), now I am limiting this wake up only to rcu_barrier() as
  requested by Paul.
- Fixed checkpatch and build robot issues.
- Some more changes to 'lazy' parameter passing and consolidation of segcblist
  functions.
- more testing via rcutorture and rcuscale.

Note that these tests were run on v2 patches, I am expecting similar power
improvements however I've not yet tested power.

Following are power savings we saw on top of RCU_NOCB_CPU on an Intel platform
in v2.  The observation is that due to a 'trickle down' effect of RCU
callbacks, the system is very lightly loaded but constantly running few RCU
callbacks very often. This confuses the power management hardware that the
system is active, when it is in fact idle.

For example, when ChromeOS screen is off and user is not doing anything on the
system, we can see big power savings.
Before:
Pk%pc10 = 72.13
PkgWatt = 0.58
CorWatt = 0.04

After:
Pk%pc10 = 81.28
PkgWatt = 0.41
CorWatt = 0.03

Further, when ChromeOS screen is ON but system is idle or lightly loaded, we
can see that the display pipeline is constantly doing RCU callback queuing due
to open/close of file descriptors associated with graphics buffers. This is
attributed to the file_free_rcu() path which this patch series also touches.

On memory pressure, timeout or queue growing too big, we initiate a flush of of
the bypass lists holding the lazy CBs.

Similar results can be achieved by increasing jiffies_till_first_fqs, however
that also has the effect of slowing down RCU. Especially I saw huge slow down
of function graph tracer when increasing that. That may be possible to fix via
rcu_expedited=1 boot parameter, however call_rcu_lazy() provides another option
over slowing down ALL call_rcu() globally. Further using jiffies_till_first_fqs
approach will still cause a wake up of the main RCU GP kthread, with this work
we delay even those wakeups.

One drawback of this series is, if another frequent RCU callback creeps up in
the future, that's not lazy, then that will again hurt the power. However, I
believe identifying and fixing those is a more reasonable approach than slowing
RCU down for the whole system.

Disclaimer: I have intentionally not CC'd other subsystem maintainers (like
net, fs) to keep noise low and will CC them in the future after 1 or 2 rounds
of review and agreements.

Joel Fernandes (Google) (4):
  rcu: Introduce call_rcu_lazy() API implementation
  rcuscale: Add laziness and kfree tests
  fs: Move call_rcu() to call_rcu_lazy() in some paths
  rcutorture: Add test code for call_rcu_lazy()

Vineeth Pillai (1):
  rcu: shrinker for lazy rcu

 fs/dcache.c                                   |   4 +-
 fs/eventpoll.c                                |   2 +-
 fs/file_table.c                               |   2 +-
 fs/inode.c                                    |   2 +-
 include/linux/rcu_segcblist.h                 |   1 +
 include/linux/rcupdate.h                      |   6 +
 kernel/rcu/Kconfig                            |   8 +
 kernel/rcu/rcu.h                              |  12 +
 kernel/rcu/rcu_segcblist.c                    |  15 +-
 kernel/rcu/rcu_segcblist.h                    |  20 +-
 kernel/rcu/rcuscale.c                         |  74 +++++-
 kernel/rcu/rcutorture.c                       |  60 ++++-
 kernel/rcu/tree.c                             | 132 ++++++----
 kernel/rcu/tree.h                             |  10 +-
 kernel/rcu/tree_nocb.h                        | 239 ++++++++++++++----
 .../selftests/rcutorture/configs/rcu/TREE11   |  18 ++
 .../rcutorture/configs/rcu/TREE11.boot        |   8 +
 17 files changed, 508 insertions(+), 105 deletions(-)
 create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/TREE11
 create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/TREE11.boot

-- 
2.37.0.144.g8ac04bfd2-goog

[PATCH 1/5] rcu: Introduce call_rcu_lazy() API implementation

[Joel Fernandes (Google)]

Implement timer-based RCU lazy callback batching. The batch is flushed
whenever a certain amount of time has passed, or the batch on a
particular CPU grows too big. Also memory pressure will flush it in a
future patch.

To handle several corner cases automagically (such as rcu_barrier() and
hotplug), we re-use bypass lists to handle lazy CBs. The bypass list
length has the lazy CB length included in it. A separate lazy CB length
counter is also introduced to keep track of the number of lazy CBs.

Suggested-by: Paul McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 include/linux/rcu_segcblist.h |   1 +
 include/linux/rcupdate.h      |   6 ++
 kernel/rcu/Kconfig            |   8 ++
 kernel/rcu/rcu.h              |  11 ++
 kernel/rcu/rcu_segcblist.c    |  15 ++-
 kernel/rcu/rcu_segcblist.h    |  20 +++-
 kernel/rcu/tree.c             | 131 +++++++++++++++---------
 kernel/rcu/tree.h             |  10 +-
 kernel/rcu/tree_nocb.h        | 185 ++++++++++++++++++++++++++--------
 9 files changed, 290 insertions(+), 97 deletions(-)

diff --git a/include/linux/rcu_segcblist.h b/include/linux/rcu_segcblist.h
index 659d13a7ddaa..9a992707917b 100644
--- a/include/linux/rcu_segcblist.h
+++ b/include/linux/rcu_segcblist.h
@@ -22,6 +22,7 @@ struct rcu_cblist {
 	struct rcu_head *head;
 	struct rcu_head **tail;
 	long len;
+	long lazy_len;
 };
 
 #define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head }
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 1a32036c918c..9191a3d88087 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -82,6 +82,12 @@ static inline int rcu_preempt_depth(void)
 
 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 
+#ifdef CONFIG_RCU_LAZY
+void call_rcu_lazy(struct rcu_head *head, rcu_callback_t func);
+#else
+#define call_rcu_lazy(head, func) call_rcu(head, func)
+#endif
+
 /* Internal to kernel */
 void rcu_init(void);
 extern int rcu_scheduler_active;
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index 27aab870ae4c..779b6e84006b 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -293,4 +293,12 @@ config TASKS_TRACE_RCU_READ_MB
 	  Say N here if you hate read-side memory barriers.
 	  Take the default if you are unsure.
 
+config RCU_LAZY
+	bool "RCU callback lazy invocation functionality"
+	depends on RCU_NOCB_CPU
+	default n
+	help
+	  To save power, batch RCU callbacks and flush after delay, memory
+	  pressure or callback list growing too big.
+
 endmenu # "RCU Subsystem"
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 4916077119f3..8e7ff7c18072 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -472,6 +472,16 @@ void do_trace_rcu_torture_read(const char *rcutorturename,
 			       unsigned long c_old,
 			       unsigned long c);
 void rcu_gp_set_torture_wait(int duration);
+void rcu_force_call_rcu_to_lazy(bool force);
+
+#if defined(CONFIG_RCU_LAZY)
+unsigned long rcu_lazy_get_jiffies_till_flush(void);
+void rcu_lazy_set_jiffies_till_flush(unsigned long j);
+#else
+static inline unsigned long rcu_lazy_get_jiffies_till_flush(void) { return 0; }
+static inline void rcu_lazy_set_jiffies_till_flush(unsigned long j) { }
+#endif
+
 #else
 static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
 					  int *flags, unsigned long *gp_seq)
@@ -490,6 +500,7 @@ void do_trace_rcu_torture_read(const char *rcutorturename,
 	do { } while (0)
 #endif
 static inline void rcu_gp_set_torture_wait(int duration) { }
+static inline void rcu_force_call_rcu_to_lazy(bool force) { }
 #endif
 
 #if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST)
diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
index c54ea2b6a36b..776647cd2d6c 100644
--- a/kernel/rcu/rcu_segcblist.c
+++ b/kernel/rcu/rcu_segcblist.c
@@ -20,16 +20,21 @@ void rcu_cblist_init(struct rcu_cblist *rclp)
 	rclp->head = NULL;
 	rclp->tail = &rclp->head;
 	rclp->len = 0;
+	rclp->lazy_len = 0;
 }
 
 /*
  * Enqueue an rcu_head structure onto the specified callback list.
  */
-void rcu_cblist_enqueue(struct rcu_cblist *rclp, struct rcu_head *rhp)
+void rcu_cblist_enqueue(struct rcu_cblist *rclp, struct rcu_head *rhp,
+			bool lazy)
 {
 	*rclp->tail = rhp;
 	rclp->tail = &rhp->next;
 	WRITE_ONCE(rclp->len, rclp->len + 1);
+
+	if (IS_ENABLED(CONFIG_RCU_LAZY) && lazy)
+		WRITE_ONCE(rclp->lazy_len, rclp->lazy_len + 1);
 }
 
 /*
@@ -38,11 +43,12 @@ void rcu_cblist_enqueue(struct rcu_cblist *rclp, struct rcu_head *rhp)
  * element of the second rcu_cblist structure, but ensuring that the second
  * rcu_cblist structure, if initially non-empty, always appears non-empty
  * throughout the process.  If rdp is NULL, the second rcu_cblist structure
- * is instead initialized to empty.
+ * is instead initialized to empty. Also account for lazy_len for lazy CBs.
  */
 void rcu_cblist_flush_enqueue(struct rcu_cblist *drclp,
 			      struct rcu_cblist *srclp,
-			      struct rcu_head *rhp)
+			      struct rcu_head *rhp,
+			      bool lazy)
 {
 	drclp->head = srclp->head;
 	if (drclp->head)
@@ -58,6 +64,9 @@ void rcu_cblist_flush_enqueue(struct rcu_cblist *drclp,
 		srclp->tail = &rhp->next;
 		WRITE_ONCE(srclp->len, 1);
 	}
+
+	if (IS_ENABLED(CONFIG_RCU_LAZY) && rhp && lazy)
+		WRITE_ONCE(srclp->lazy_len, 1);
 }
 
 /*
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index 431cee212467..8e90b34adb00 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -15,14 +15,30 @@ static inline long rcu_cblist_n_cbs(struct rcu_cblist *rclp)
 	return READ_ONCE(rclp->len);
 }
 
+/* Return number of callbacks in the specified callback list. */
+static inline long rcu_cblist_n_lazy_cbs(struct rcu_cblist *rclp)
+{
+	if (IS_ENABLED(CONFIG_RCU_LAZY))
+		return READ_ONCE(rclp->lazy_len);
+	return 0;
+}
+
+static inline void rcu_cblist_reset_lazy_len(struct rcu_cblist *rclp)
+{
+	if (IS_ENABLED(CONFIG_RCU_LAZY))
+		WRITE_ONCE(rclp->lazy_len, 0);
+}
+
 /* Return number of callbacks in segmented callback list by summing seglen. */
 long rcu_segcblist_n_segment_cbs(struct rcu_segcblist *rsclp);
 
 void rcu_cblist_init(struct rcu_cblist *rclp);
-void rcu_cblist_enqueue(struct rcu_cblist *rclp, struct rcu_head *rhp);
+void rcu_cblist_enqueue(struct rcu_cblist *rclp, struct rcu_head *rhp,
+			bool lazy);
 void rcu_cblist_flush_enqueue(struct rcu_cblist *drclp,
 			      struct rcu_cblist *srclp,
-			      struct rcu_head *rhp);
+			      struct rcu_head *rhp,
+			      bool lazy);
 struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp);
 
 /*
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index c25ba442044a..cdbdd56e64b1 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3058,47 +3058,8 @@ static void check_cb_ovld(struct rcu_data *rdp)
 	raw_spin_unlock_rcu_node(rnp);
 }
 
-/**
- * call_rcu() - Queue an RCU callback for invocation after a grace period.
- * @head: structure to be used for queueing the RCU updates.
- * @func: actual callback function to be invoked after the grace period
- *
- * The callback function will be invoked some time after a full grace
- * period elapses, in other words after all pre-existing RCU read-side
- * critical sections have completed.  However, the callback function
- * might well execute concurrently with RCU read-side critical sections
- * that started after call_rcu() was invoked.
- *
- * RCU read-side critical sections are delimited by rcu_read_lock()
- * and rcu_read_unlock(), and may be nested.  In addition, but only in
- * v5.0 and later, regions of code across which interrupts, preemption,
- * or softirqs have been disabled also serve as RCU read-side critical
- * sections.  This includes hardware interrupt handlers, softirq handlers,
- * and NMI handlers.
- *
- * Note that all CPUs must agree that the grace period extended beyond
- * all pre-existing RCU read-side critical section.  On systems with more
- * than one CPU, this means that when "func()" is invoked, each CPU is
- * guaranteed to have executed a full memory barrier since the end of its
- * last RCU read-side critical section whose beginning preceded the call
- * to call_rcu().  It also means that each CPU executing an RCU read-side
- * critical section that continues beyond the start of "func()" must have
- * executed a memory barrier after the call_rcu() but before the beginning
- * of that RCU read-side critical section.  Note that these guarantees
- * include CPUs that are offline, idle, or executing in user mode, as
- * well as CPUs that are executing in the kernel.
- *
- * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
- * resulting RCU callback function "func()", then both CPU A and CPU B are
- * guaranteed to execute a full memory barrier during the time interval
- * between the call to call_rcu() and the invocation of "func()" -- even
- * if CPU A and CPU B are the same CPU (but again only if the system has
- * more than one CPU).
- *
- * Implementation of these memory-ordering guarantees is described here:
- * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
- */
-void call_rcu(struct rcu_head *head, rcu_callback_t func)
+static void
+__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy)
 {
 	static atomic_t doublefrees;
 	unsigned long flags;
@@ -3139,7 +3100,7 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func)
 	}
 
 	check_cb_ovld(rdp);
-	if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags))
+	if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy))
 		return; // Enqueued onto ->nocb_bypass, so just leave.
 	// If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock.
 	rcu_segcblist_enqueue(&rdp->cblist, head);
@@ -3161,8 +3122,87 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func)
 		local_irq_restore(flags);
 	}
 }
-EXPORT_SYMBOL_GPL(call_rcu);
 
+#ifdef CONFIG_RCU_LAZY
+/**
+ * call_rcu_lazy() - Lazily queue RCU callback for invocation after grace period.
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual callback function to be invoked after the grace period
+ *
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all pre-existing RCU read-side
+ * critical sections have completed.
+ *
+ * Use this API instead of call_rcu() if you don't mind the callback being
+ * invoked after very long periods of time on systems without memory pressure
+ * and on systems which are lightly loaded or mostly idle.
+ *
+ * Other than the extra delay in callbacks being invoked, this function is
+ * identical to, and reuses call_rcu()'s logic. Refer to call_rcu() for more
+ * details about memory ordering and other functionality.
+ */
+void call_rcu_lazy(struct rcu_head *head, rcu_callback_t func)
+{
+	return __call_rcu_common(head, func, true);
+}
+EXPORT_SYMBOL_GPL(call_rcu_lazy);
+#endif
+
+static bool force_call_rcu_to_lazy;
+
+void rcu_force_call_rcu_to_lazy(bool force)
+{
+	if (IS_ENABLED(CONFIG_RCU_SCALE_TEST))
+		WRITE_ONCE(force_call_rcu_to_lazy, force);
+}
+EXPORT_SYMBOL_GPL(rcu_force_call_rcu_to_lazy);
+
+/**
+ * call_rcu() - Queue an RCU callback for invocation after a grace period.
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual callback function to be invoked after the grace period
+ *
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all pre-existing RCU read-side
+ * critical sections have completed.  However, the callback function
+ * might well execute concurrently with RCU read-side critical sections
+ * that started after call_rcu() was invoked.
+ *
+ * RCU read-side critical sections are delimited by rcu_read_lock()
+ * and rcu_read_unlock(), and may be nested.  In addition, but only in
+ * v5.0 and later, regions of code across which interrupts, preemption,
+ * or softirqs have been disabled also serve as RCU read-side critical
+ * sections.  This includes hardware interrupt handlers, softirq handlers,
+ * and NMI handlers.
+ *
+ * Note that all CPUs must agree that the grace period extended beyond
+ * all pre-existing RCU read-side critical section.  On systems with more
+ * than one CPU, this means that when "func()" is invoked, each CPU is
+ * guaranteed to have executed a full memory barrier since the end of its
+ * last RCU read-side critical section whose beginning preceded the call
+ * to call_rcu().  It also means that each CPU executing an RCU read-side
+ * critical section that continues beyond the start of "func()" must have
+ * executed a memory barrier after the call_rcu() but before the beginning
+ * of that RCU read-side critical section.  Note that these guarantees
+ * include CPUs that are offline, idle, or executing in user mode, as
+ * well as CPUs that are executing in the kernel.
+ *
+ * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
+ * resulting RCU callback function "func()", then both CPU A and CPU B are
+ * guaranteed to execute a full memory barrier during the time interval
+ * between the call to call_rcu() and the invocation of "func()" -- even
+ * if CPU A and CPU B are the same CPU (but again only if the system has
+ * more than one CPU).
+ *
+ * Implementation of these memory-ordering guarantees is described here:
+ * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
+ */
+void call_rcu(struct rcu_head *head, rcu_callback_t func)
+{
+	return __call_rcu_common(head, func, force_call_rcu_to_lazy);
+
+}
+EXPORT_SYMBOL_GPL(call_rcu);
 
 /* Maximum number of jiffies to wait before draining a batch. */
 #define KFREE_DRAIN_JIFFIES (HZ / 50)
@@ -4056,7 +4096,8 @@ static void rcu_barrier_entrain(struct rcu_data *rdp)
 	rdp->barrier_head.func = rcu_barrier_callback;
 	debug_rcu_head_queue(&rdp->barrier_head);
 	rcu_nocb_lock(rdp);
-	WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies));
+	WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false,
+		     /* wake gp thread */ true));
 	if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head)) {
 		atomic_inc(&rcu_state.barrier_cpu_count);
 	} else {
@@ -4476,7 +4517,7 @@ void rcutree_migrate_callbacks(int cpu)
 	my_rdp = this_cpu_ptr(&rcu_data);
 	my_rnp = my_rdp->mynode;
 	rcu_nocb_lock(my_rdp); /* irqs already disabled. */
-	WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies));
+	WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies, false, false));
 	raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */
 	/* Leverage recent GPs and set GP for new callbacks. */
 	needwake = rcu_advance_cbs(my_rnp, rdp) ||
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 2ccf5845957d..7b1ddee6a159 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -267,8 +267,9 @@ struct rcu_data {
 /* Values for nocb_defer_wakeup field in struct rcu_data. */
 #define RCU_NOCB_WAKE_NOT	0
 #define RCU_NOCB_WAKE_BYPASS	1
-#define RCU_NOCB_WAKE		2
-#define RCU_NOCB_WAKE_FORCE	3
+#define RCU_NOCB_WAKE_LAZY	2
+#define RCU_NOCB_WAKE		3
+#define RCU_NOCB_WAKE_FORCE	4
 
 #define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500))
 					/* For jiffies_till_first_fqs and */
@@ -436,9 +437,10 @@ static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp);
 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq);
 static void rcu_init_one_nocb(struct rcu_node *rnp);
 static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
-				  unsigned long j);
+				  unsigned long j, bool lazy, bool wakegp);
 static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
-				bool *was_alldone, unsigned long flags);
+				bool *was_alldone, unsigned long flags,
+				bool lazy);
 static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
 				 unsigned long flags);
 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level);
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index e369efe94fda..61b1409bd4d6 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -256,6 +256,31 @@ static bool wake_nocb_gp(struct rcu_data *rdp, bool force)
 	return __wake_nocb_gp(rdp_gp, rdp, force, flags);
 }
 
+/*
+ * LAZY_FLUSH_JIFFIES decides the maximum amount of time that
+ * can elapse before lazy callbacks are flushed. Lazy callbacks
+ * could be flushed much earlier for a number of other reasons
+ * however, LAZY_FLUSH_JIFFIES will ensure no lazy callbacks are
+ * left unsubmitted to RCU after those many jiffies.
+ */
+#define LAZY_FLUSH_JIFFIES (10 * HZ)
+unsigned long jiffies_till_flush = LAZY_FLUSH_JIFFIES;
+
+#ifdef CONFIG_RCU_LAZY
+// To be called only from test code.
+void rcu_lazy_set_jiffies_till_flush(unsigned long jif)
+{
+	jiffies_till_flush = jif;
+}
+EXPORT_SYMBOL(rcu_lazy_set_jiffies_till_flush);
+
+unsigned long rcu_lazy_get_jiffies_till_flush(void)
+{
+	return jiffies_till_flush;
+}
+EXPORT_SYMBOL(rcu_lazy_get_jiffies_till_flush);
+#endif
+
 /*
  * Arrange to wake the GP kthread for this NOCB group at some future
  * time when it is safe to do so.
@@ -265,6 +290,7 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
 {
 	unsigned long flags;
 	struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
+	unsigned long mod_jif = 0;
 
 	raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
 
@@ -272,16 +298,32 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
 	 * Bypass wakeup overrides previous deferments. In case
 	 * of callback storm, no need to wake up too early.
 	 */
-	if (waketype == RCU_NOCB_WAKE_BYPASS) {
-		mod_timer(&rdp_gp->nocb_timer, jiffies + 2);
-		WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
-	} else {
+	switch (waketype) {
+	case RCU_NOCB_WAKE_LAZY:
+		if (rdp->nocb_defer_wakeup != RCU_NOCB_WAKE_LAZY)
+			mod_jif = jiffies_till_flush;
+		break;
+
+	case RCU_NOCB_WAKE_BYPASS:
+		mod_jif = 2;
+		break;
+
+	case RCU_NOCB_WAKE:
+	case RCU_NOCB_WAKE_FORCE:
+		// If the type of deferred wake is "stronger"
+		// than it was before, make it wake up the soonest.
 		if (rdp_gp->nocb_defer_wakeup < RCU_NOCB_WAKE)
-			mod_timer(&rdp_gp->nocb_timer, jiffies + 1);
-		if (rdp_gp->nocb_defer_wakeup < waketype)
-			WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
+			mod_jif = 1;
+		break;
 	}
 
+	if (mod_jif)
+		mod_timer(&rdp_gp->nocb_timer, jiffies + mod_jif);
+
+	// If new type of wake up is stronger than before, promote.
+	if (rdp_gp->nocb_defer_wakeup < waketype)
+		WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
+
 	raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
 
 	trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason);
@@ -296,7 +338,7 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
  * Note that this function always returns true if rhp is NULL.
  */
 static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
-				     unsigned long j)
+				     unsigned long j, bool lazy)
 {
 	struct rcu_cblist rcl;
 
@@ -310,7 +352,9 @@ static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 	/* Note: ->cblist.len already accounts for ->nocb_bypass contents. */
 	if (rhp)
 		rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
-	rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp);
+
+	/* The lazy CBs are being flushed, but a new one might be enqueued. */
+	rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp, lazy);
 	rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl);
 	WRITE_ONCE(rdp->nocb_bypass_first, j);
 	rcu_nocb_bypass_unlock(rdp);
@@ -326,13 +370,20 @@ static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
  * Note that this function always returns true if rhp is NULL.
  */
 static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
-				  unsigned long j)
+				  unsigned long j, bool lazy, bool wake_gp)
 {
+	bool ret;
+
 	if (!rcu_rdp_is_offloaded(rdp))
 		return true;
 	rcu_lockdep_assert_cblist_protected(rdp);
 	rcu_nocb_bypass_lock(rdp);
-	return rcu_nocb_do_flush_bypass(rdp, rhp, j);
+	ret = rcu_nocb_do_flush_bypass(rdp, rhp, j, lazy);
+
+	if (wake_gp)
+		wake_nocb_gp(rdp, true);
+
+	return ret;
 }
 
 /*
@@ -345,7 +396,7 @@ static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j)
 	if (!rcu_rdp_is_offloaded(rdp) ||
 	    !rcu_nocb_bypass_trylock(rdp))
 		return;
-	WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j));
+	WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j, false));
 }
 
 /*
@@ -367,12 +418,14 @@ static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j)
  * there is only one CPU in operation.
  */
 static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
-				bool *was_alldone, unsigned long flags)
+				bool *was_alldone, unsigned long flags,
+				bool lazy)
 {
 	unsigned long c;
 	unsigned long cur_gp_seq;
 	unsigned long j = jiffies;
 	long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
+	long n_lazy_cbs = rcu_cblist_n_lazy_cbs(&rdp->nocb_bypass);
 
 	lockdep_assert_irqs_disabled();
 
@@ -414,30 +467,37 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 	}
 	WRITE_ONCE(rdp->nocb_nobypass_count, c);
 
-	// If there hasn't yet been all that many ->cblist enqueues
-	// this jiffy, tell the caller to enqueue onto ->cblist.  But flush
-	// ->nocb_bypass first.
-	if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy) {
+	// If caller passed a non-lazy CB and there hasn't yet been all that
+	// many ->cblist enqueues this jiffy, tell the caller to enqueue it
+	// onto ->cblist.  But flush ->nocb_bypass first. Also do so, if total
+	// number of CBs (lazy + non-lazy) grows too much.
+	//
+	// Note that if the bypass list has lazy CBs, and the main list is
+	// empty, and rhp happens to be non-lazy, then we end up flushing all
+	// the lazy CBs to the main list as well. That's the right thing to do,
+	// since we are kick-starting RCU GP processing anyway for the non-lazy
+	// one, we can just reuse that GP for the already queued-up lazy ones.
+	if ((rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy && !lazy) ||
+	    (lazy && n_lazy_cbs >= qhimark)) {
 		rcu_nocb_lock(rdp);
 		*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
 		if (*was_alldone)
 			trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
-					    TPS("FirstQ"));
-		WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j));
+					    lazy ? TPS("FirstLazyQ") : TPS("FirstQ"));
+		WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j, lazy, false));
 		WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
 		return false; // Caller must enqueue the callback.
 	}
 
 	// If ->nocb_bypass has been used too long or is too full,
 	// flush ->nocb_bypass to ->cblist.
-	if ((ncbs && j != READ_ONCE(rdp->nocb_bypass_first)) ||
-	    ncbs >= qhimark) {
+	if ((ncbs && j != READ_ONCE(rdp->nocb_bypass_first)) || ncbs >= qhimark) {
 		rcu_nocb_lock(rdp);
-		if (!rcu_nocb_flush_bypass(rdp, rhp, j)) {
+		if (!rcu_nocb_flush_bypass(rdp, rhp, j, lazy, false)) {
 			*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
 			if (*was_alldone)
 				trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
-						    TPS("FirstQ"));
+						    lazy ? TPS("FirstLazyQ") : TPS("FirstQ"));
 			WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
 			return false; // Caller must enqueue the callback.
 		}
@@ -455,12 +515,18 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 	rcu_nocb_wait_contended(rdp);
 	rcu_nocb_bypass_lock(rdp);
 	ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
+	n_lazy_cbs = rcu_cblist_n_lazy_cbs(&rdp->nocb_bypass);
 	rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
-	rcu_cblist_enqueue(&rdp->nocb_bypass, rhp);
+	rcu_cblist_enqueue(&rdp->nocb_bypass, rhp, lazy);
+
 	if (!ncbs) {
 		WRITE_ONCE(rdp->nocb_bypass_first, j);
-		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstBQ"));
+		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
+				    lazy ? TPS("FirstLazyBQ") : TPS("FirstBQ"));
+	} else if (!n_lazy_cbs && lazy) {
+		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstLazyBQ"));
 	}
+
 	rcu_nocb_bypass_unlock(rdp);
 	smp_mb(); /* Order enqueue before wake. */
 	if (ncbs) {
@@ -493,7 +559,7 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
 {
 	unsigned long cur_gp_seq;
 	unsigned long j;
-	long len;
+	long len, lazy_len, bypass_len;
 	struct task_struct *t;
 
 	// If we are being polled or there is no kthread, just leave.
@@ -506,9 +572,16 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
 	}
 	// Need to actually to a wakeup.
 	len = rcu_segcblist_n_cbs(&rdp->cblist);
+	bypass_len = rcu_cblist_n_cbs(&rdp->nocb_bypass);
+	lazy_len = rcu_cblist_n_lazy_cbs(&rdp->nocb_bypass);
 	if (was_alldone) {
 		rdp->qlen_last_fqs_check = len;
-		if (!irqs_disabled_flags(flags)) {
+		// Only lazy CBs in bypass list
+		if (lazy_len && bypass_len == lazy_len) {
+			rcu_nocb_unlock_irqrestore(rdp, flags);
+			wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_LAZY,
+					   TPS("WakeLazy"));
+		} else if (!irqs_disabled_flags(flags)) {
 			/* ... if queue was empty ... */
 			rcu_nocb_unlock_irqrestore(rdp, flags);
 			wake_nocb_gp(rdp, false);
@@ -599,8 +672,8 @@ static inline bool nocb_gp_update_state_deoffloading(struct rcu_data *rdp,
  */
 static void nocb_gp_wait(struct rcu_data *my_rdp)
 {
-	bool bypass = false;
-	long bypass_ncbs;
+	bool bypass = false, lazy = false;
+	long bypass_ncbs, lazy_ncbs;
 	int __maybe_unused cpu = my_rdp->cpu;
 	unsigned long cur_gp_seq;
 	unsigned long flags;
@@ -636,6 +709,7 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
 	 */
 	list_for_each_entry_rcu(rdp, &my_rdp->nocb_head_rdp, nocb_entry_rdp, 1) {
 		bool needwake_state = false;
+		bool flush_bypass = false;
 
 		if (!nocb_gp_enabled_cb(rdp))
 			continue;
@@ -648,22 +722,37 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
 			continue;
 		}
 		bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
-		if (bypass_ncbs &&
+		lazy_ncbs = rcu_cblist_n_lazy_cbs(&rdp->nocb_bypass);
+
+		if (lazy_ncbs &&
+		    (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + jiffies_till_flush) ||
+		     bypass_ncbs > 2 * qhimark)) {
+			flush_bypass = true;
+		} else if (bypass_ncbs && (lazy_ncbs != bypass_ncbs) &&
 		    (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) ||
 		     bypass_ncbs > 2 * qhimark)) {
-			// Bypass full or old, so flush it.
-			(void)rcu_nocb_try_flush_bypass(rdp, j);
-			bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
+			flush_bypass = true;
 		} else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) {
 			rcu_nocb_unlock_irqrestore(rdp, flags);
 			if (needwake_state)
 				swake_up_one(&rdp->nocb_state_wq);
 			continue; /* No callbacks here, try next. */
 		}
+
+		if (flush_bypass) {
+			// Bypass full or old, so flush it.
+			(void)rcu_nocb_try_flush_bypass(rdp, j);
+			bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
+			lazy_ncbs = rcu_cblist_n_lazy_cbs(&rdp->nocb_bypass);
+		}
+
 		if (bypass_ncbs) {
 			trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
-					    TPS("Bypass"));
-			bypass = true;
+				    bypass_ncbs == lazy_ncbs ? TPS("Lazy") : TPS("Bypass"));
+			if (bypass_ncbs == lazy_ncbs)
+				lazy = true;
+			else
+				bypass = true;
 		}
 		rnp = rdp->mynode;
 
@@ -713,12 +802,21 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
 	my_rdp->nocb_gp_gp = needwait_gp;
 	my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
 
-	if (bypass && !rcu_nocb_poll) {
-		// At least one child with non-empty ->nocb_bypass, so set
-		// timer in order to avoid stranding its callbacks.
-		wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_BYPASS,
-				   TPS("WakeBypassIsDeferred"));
+	// At least one child with non-empty ->nocb_bypass, so set
+	// timer in order to avoid stranding its callbacks.
+	if (!rcu_nocb_poll) {
+		// If bypass list only has lazy CBs. Add a deferred
+		// lazy wake up.
+		if (lazy && !bypass) {
+			wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_LAZY,
+					TPS("WakeLazyIsDeferred"));
+		// Otherwise add a deferred bypass wake up.
+		} else if (bypass) {
+			wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_BYPASS,
+					TPS("WakeBypassIsDeferred"));
+		}
 	}
+
 	if (rcu_nocb_poll) {
 		/* Polling, so trace if first poll in the series. */
 		if (gotcbs)
@@ -999,7 +1097,7 @@ static long rcu_nocb_rdp_deoffload(void *arg)
 	 * return false, which means that future calls to rcu_nocb_try_bypass()
 	 * will refuse to put anything into the bypass.
 	 */
-	WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies));
+	WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false, false));
 	/*
 	 * Start with invoking rcu_core() early. This way if the current thread
 	 * happens to preempt an ongoing call to rcu_core() in the middle,
@@ -1500,13 +1598,14 @@ static void rcu_init_one_nocb(struct rcu_node *rnp)
 }
 
 static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
-				  unsigned long j)
+				  unsigned long j, bool lazy, bool wakegp)
 {
 	return true;
 }
 
 static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
-				bool *was_alldone, unsigned long flags)
+				bool *was_alldone, unsigned long flags,
+				bool lazy)
 {
 	return false;
 }
-- 
2.37.0.144.g8ac04bfd2-goog

[PATCH 2/5] rcu: shrinker for lazy rcu

[Joel Fernandes (Google)]

From: Vineeth Pillai <vineeth@bitbyteword.org>

The shrinker is used to speed up the free'ing of memory potentially held
by RCU lazy callbacks. RCU kernel module test cases show this to be
effective. Test is introduced in a later patch.

Signed-off-by: Vineeth Pillai <vineeth@bitbyteword.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 kernel/rcu/tree_nocb.h | 52 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 61b1409bd4d6..f8d7255f4f0a 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1249,6 +1249,55 @@ int rcu_nocb_cpu_offload(int cpu)
 }
 EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
 
+static unsigned long
+lazy_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
+{
+	int cpu;
+	unsigned long count = 0;
+
+	/* Snapshot count of all CPUs */
+	for_each_possible_cpu(cpu) {
+		struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+
+		count += rcu_cblist_n_lazy_cbs(&rdp->nocb_bypass);
+	}
+
+	return count ? count : SHRINK_EMPTY;
+}
+
+static unsigned long
+lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
+{
+	int cpu;
+	unsigned long flags;
+	unsigned long count = 0;
+
+	/* Snapshot count of all CPUs */
+	for_each_possible_cpu(cpu) {
+		struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+		int _count = rcu_cblist_n_lazy_cbs(&rdp->nocb_bypass);
+
+		if (_count == 0)
+			continue;
+		rcu_nocb_lock_irqsave(rdp, flags);
+		rcu_cblist_reset_lazy_len(&rdp->nocb_bypass);
+		rcu_nocb_unlock_irqrestore(rdp, flags);
+		wake_nocb_gp(rdp, false);
+		sc->nr_to_scan -= _count;
+		count += _count;
+		if (sc->nr_to_scan <= 0)
+			break;
+	}
+	return count ? count : SHRINK_STOP;
+}
+
+static struct shrinker lazy_rcu_shrinker = {
+	.count_objects = lazy_rcu_shrink_count,
+	.scan_objects = lazy_rcu_shrink_scan,
+	.batch = 0,
+	.seeks = DEFAULT_SEEKS,
+};
+
 void __init rcu_init_nohz(void)
 {
 	int cpu;
@@ -1286,6 +1335,9 @@ void __init rcu_init_nohz(void)
 	if (!rcu_state.nocb_is_setup)
 		return;
 
+	if (register_shrinker(&lazy_rcu_shrinker))
+		pr_err("Failed to register lazy_rcu shrinker!\n");
+
 #if defined(CONFIG_NO_HZ_FULL)
 	if (tick_nohz_full_running)
 		cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
-- 
2.37.0.144.g8ac04bfd2-goog

[PATCH 3/5] rcuscale: Add laziness and kfree tests

[Joel Fernandes (Google)]

We had 2 tests to rcuscale, one is a startup test to check whether we
are not too lazy or too hard working. Two, emulate kfree_rcu() itself to
use call_rcu_lazy() and check memory pressure. In my testing,
call_rcu_lazy() does well to keep memory pressure under control, similar
to kfree_rcu().

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 kernel/rcu/rcuscale.c | 74 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 73 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
index 277a5bfb37d4..ed5544227f4d 100644
--- a/kernel/rcu/rcuscale.c
+++ b/kernel/rcu/rcuscale.c
@@ -95,6 +95,7 @@ torture_param(int, verbose, 1, "Enable verbose debugging printk()s");
 torture_param(int, writer_holdoff, 0, "Holdoff (us) between GPs, zero to disable");
 torture_param(int, kfree_rcu_test, 0, "Do we run a kfree_rcu() scale test?");
 torture_param(int, kfree_mult, 1, "Multiple of kfree_obj size to allocate.");
+torture_param(int, kfree_rcu_by_lazy, 0, "Use call_rcu_lazy() to emulate kfree_rcu()?");
 
 static char *scale_type = "rcu";
 module_param(scale_type, charp, 0444);
@@ -658,6 +659,14 @@ struct kfree_obj {
 	struct rcu_head rh;
 };
 
+/* Used if doing RCU-kfree'ing via call_rcu_lazy(). */
+static void kfree_rcu_lazy(struct rcu_head *rh)
+{
+	struct kfree_obj *obj = container_of(rh, struct kfree_obj, rh);
+
+	kfree(obj);
+}
+
 static int
 kfree_scale_thread(void *arg)
 {
@@ -695,6 +704,11 @@ kfree_scale_thread(void *arg)
 			if (!alloc_ptr)
 				return -ENOMEM;
 
+			if (kfree_rcu_by_lazy) {
+				call_rcu_lazy(&(alloc_ptr->rh), kfree_rcu_lazy);
+				continue;
+			}
+
 			// By default kfree_rcu_test_single and kfree_rcu_test_double are
 			// initialized to false. If both have the same value (false or true)
 			// both are randomly tested, otherwise only the one with value true
@@ -737,6 +751,9 @@ kfree_scale_cleanup(void)
 {
 	int i;
 
+	if (kfree_rcu_by_lazy)
+		rcu_force_call_rcu_to_lazy(false);
+
 	if (torture_cleanup_begin())
 		return;
 
@@ -766,11 +783,64 @@ kfree_scale_shutdown(void *arg)
 	return -EINVAL;
 }
 
+// Used if doing RCU-kfree'ing via call_rcu_lazy().
+static unsigned long jiffies_at_lazy_cb;
+static struct rcu_head lazy_test1_rh;
+static int rcu_lazy_test1_cb_called;
+static void call_rcu_lazy_test1(struct rcu_head *rh)
+{
+	jiffies_at_lazy_cb = jiffies;
+	WRITE_ONCE(rcu_lazy_test1_cb_called, 1);
+}
+
 static int __init
 kfree_scale_init(void)
 {
 	long i;
 	int firsterr = 0;
+	unsigned long orig_jif, jif_start;
+
+	// If lazy-rcu based kfree'ing is requested, then for kernels that
+	// support it, force all call_rcu() to call_rcu_lazy() so that non-lazy
+	// CBs do not remove laziness of the lazy ones (since the test tries to
+	// stress call_rcu_lazy() for OOM).
+	//
+	// Also, do a quick self-test to ensure laziness is as much as
+	// expected.
+	if (kfree_rcu_by_lazy && !IS_ENABLED(CONFIG_RCU_LAZY)) {
+		pr_alert("CONFIG_RCU_LAZY is disabled, falling back to kfree_rcu() "
+			 "for delayed RCU kfree'ing\n");
+		kfree_rcu_by_lazy = 0;
+	}
+
+	if (kfree_rcu_by_lazy) {
+		/* do a test to check the timeout. */
+		orig_jif = rcu_lazy_get_jiffies_till_flush();
+
+		rcu_force_call_rcu_to_lazy(true);
+		rcu_lazy_set_jiffies_till_flush(2 * HZ);
+		rcu_barrier();
+
+		jif_start = jiffies;
+		jiffies_at_lazy_cb = 0;
+		call_rcu_lazy(&lazy_test1_rh, call_rcu_lazy_test1);
+
+		smp_cond_load_relaxed(&rcu_lazy_test1_cb_called, VAL == 1);
+
+		rcu_lazy_set_jiffies_till_flush(orig_jif);
+
+		if (WARN_ON_ONCE(jiffies_at_lazy_cb - jif_start < 2 * HZ)) {
+			pr_alert("ERROR: Lazy CBs are not being lazy as expected!\n");
+			WARN_ON_ONCE(1);
+			return -1;
+		}
+
+		if (WARN_ON_ONCE(jiffies_at_lazy_cb - jif_start > 3 * HZ)) {
+			pr_alert("ERROR: Lazy CBs are being too lazy!\n");
+			WARN_ON_ONCE(1);
+			return -1;
+		}
+	}
 
 	kfree_nrealthreads = compute_real(kfree_nthreads);
 	/* Start up the kthreads. */
@@ -783,7 +853,9 @@ kfree_scale_init(void)
 		schedule_timeout_uninterruptible(1);
 	}
 
-	pr_alert("kfree object size=%zu\n", kfree_mult * sizeof(struct kfree_obj));
+	pr_alert("kfree object size=%zu, kfree_rcu_by_lazy=%d\n",
+			kfree_mult * sizeof(struct kfree_obj),
+			kfree_rcu_by_lazy);
 
 	kfree_reader_tasks = kcalloc(kfree_nrealthreads, sizeof(kfree_reader_tasks[0]),
 			       GFP_KERNEL);
-- 
2.37.0.144.g8ac04bfd2-goog

[PATCH 4/5] fs: Move call_rcu() to call_rcu_lazy() in some paths

[Joel Fernandes (Google)]

This is required to prevent callbacks triggering RCU machinery too
quickly and too often, which adds more power to the system.

When testing, we found that these paths were invoked often when the
system is not doing anything (screen is ON but otherwise idle).

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 fs/dcache.c     | 4 ++--
 fs/eventpoll.c  | 2 +-
 fs/file_table.c | 2 +-
 fs/inode.c      | 2 +-
 4 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 93f4f5ee07bf..7f51bac390c8 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -366,7 +366,7 @@ static void dentry_free(struct dentry *dentry)
 	if (unlikely(dname_external(dentry))) {
 		struct external_name *p = external_name(dentry);
 		if (likely(atomic_dec_and_test(&p->u.count))) {
-			call_rcu(&dentry->d_u.d_rcu, __d_free_external);
+			call_rcu_lazy(&dentry->d_u.d_rcu, __d_free_external);
 			return;
 		}
 	}
@@ -374,7 +374,7 @@ static void dentry_free(struct dentry *dentry)
 	if (dentry->d_flags & DCACHE_NORCU)
 		__d_free(&dentry->d_u.d_rcu);
 	else
-		call_rcu(&dentry->d_u.d_rcu, __d_free);
+		call_rcu_lazy(&dentry->d_u.d_rcu, __d_free);
 }
 
 /*
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 971f98af48ff..57b3f781760c 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -729,7 +729,7 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi)
 	 * ep->mtx. The rcu read side, reverse_path_check_proc(), does not make
 	 * use of the rbn field.
 	 */
-	call_rcu(&epi->rcu, epi_rcu_free);
+	call_rcu_lazy(&epi->rcu, epi_rcu_free);
 
 	percpu_counter_dec(&ep->user->epoll_watches);
 
diff --git a/fs/file_table.c b/fs/file_table.c
index 5424e3a8df5f..417f57e9cb30 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -56,7 +56,7 @@ static inline void file_free(struct file *f)
 	security_file_free(f);
 	if (!(f->f_mode & FMODE_NOACCOUNT))
 		percpu_counter_dec(&nr_files);
-	call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
+	call_rcu_lazy(&f->f_u.fu_rcuhead, file_free_rcu);
 }
 
 /*
diff --git a/fs/inode.c b/fs/inode.c
index bd4da9c5207e..38fe040ddbd6 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -312,7 +312,7 @@ static void destroy_inode(struct inode *inode)
 			return;
 	}
 	inode->free_inode = ops->free_inode;
-	call_rcu(&inode->i_rcu, i_callback);
+	call_rcu_lazy(&inode->i_rcu, i_callback);
 }
 
 /**
-- 
2.37.0.144.g8ac04bfd2-goog

[PATCH 5/5] rcutorture: Add test code for call_rcu_lazy()

[Joel Fernandes (Google)]

We add a new RCU type to test call_rcu_lazy(). This allows us to just
override the '.call' callback. To compensate for the laziness, we force
the laziness to a small number of jiffies. The idea of this test is to
stress the new code paths for stability and ensure it at least is providing
behavior in parity with, or similar to, call_rcu(). The actual check for
amount of laziness is in another test (rcuscale).

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 kernel/rcu/rcu.h                              |  1 +
 kernel/rcu/rcutorture.c                       | 60 ++++++++++++++++++-
 kernel/rcu/tree.c                             |  1 +
 .../selftests/rcutorture/configs/rcu/CFLIST   |  1 +
 .../selftests/rcutorture/configs/rcu/TREE11   | 18 ++++++
 .../rcutorture/configs/rcu/TREE11.boot        |  8 +++
 6 files changed, 88 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/TREE11
 create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/TREE11.boot

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 8e7ff7c18072..c358387fd223 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -460,6 +460,7 @@ enum rcutorture_type {
 	RCU_TASKS_TRACING_FLAVOR,
 	RCU_TRIVIAL_FLAVOR,
 	SRCU_FLAVOR,
+	RCU_LAZY_FLAVOR,
 	INVALID_RCU_FLAVOR
 };
 
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 7120165a9342..c52cc4c064f9 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -872,6 +872,64 @@ static struct rcu_torture_ops tasks_rude_ops = {
 
 #endif // #else #ifdef CONFIG_TASKS_RUDE_RCU
 
+#ifdef CONFIG_RCU_LAZY
+
+/*
+ * Definitions for lazy RCU torture testing.
+ */
+static unsigned long orig_jiffies_till_flush;
+
+static void rcu_sync_torture_init_lazy(void)
+{
+	rcu_sync_torture_init();
+
+	orig_jiffies_till_flush = rcu_lazy_get_jiffies_till_flush();
+	rcu_lazy_set_jiffies_till_flush(50);
+}
+
+static void rcu_lazy_cleanup(void)
+{
+	rcu_lazy_set_jiffies_till_flush(orig_jiffies_till_flush);
+}
+
+static struct rcu_torture_ops rcu_lazy_ops = {
+	.ttype			= RCU_LAZY_FLAVOR,
+	.init			= rcu_sync_torture_init_lazy,
+	.cleanup		= rcu_lazy_cleanup,
+	.readlock		= rcu_torture_read_lock,
+	.read_delay		= rcu_read_delay,
+	.readunlock		= rcu_torture_read_unlock,
+	.readlock_held		= torture_readlock_not_held,
+	.get_gp_seq		= rcu_get_gp_seq,
+	.gp_diff		= rcu_seq_diff,
+	.deferred_free		= rcu_torture_deferred_free,
+	.sync			= synchronize_rcu,
+	.exp_sync		= synchronize_rcu_expedited,
+	.get_gp_state		= get_state_synchronize_rcu,
+	.start_gp_poll		= start_poll_synchronize_rcu,
+	.poll_gp_state		= poll_state_synchronize_rcu,
+	.cond_sync		= cond_synchronize_rcu,
+	.call			= call_rcu_lazy,
+	.cb_barrier		= rcu_barrier,
+	.fqs			= rcu_force_quiescent_state,
+	.stats			= NULL,
+	.gp_kthread_dbg		= show_rcu_gp_kthreads,
+	.check_boost_failed	= rcu_check_boost_fail,
+	.stall_dur		= rcu_jiffies_till_stall_check,
+	.irq_capable		= 1,
+	.can_boost		= IS_ENABLED(CONFIG_RCU_BOOST),
+	.extendables		= RCUTORTURE_MAX_EXTEND,
+	.name			= "rcu_lazy"
+};
+
+#define LAZY_OPS &rcu_lazy_ops,
+
+#else // #ifdef CONFIG_RCU_LAZY
+
+#define LAZY_OPS
+
+#endif // #else #ifdef CONFIG_RCU_LAZY
+
 
 #ifdef CONFIG_TASKS_TRACE_RCU
 
@@ -3145,7 +3203,7 @@ rcu_torture_init(void)
 	unsigned long gp_seq = 0;
 	static struct rcu_torture_ops *torture_ops[] = {
 		&rcu_ops, &rcu_busted_ops, &srcu_ops, &srcud_ops, &busted_srcud_ops,
-		TASKS_OPS TASKS_RUDE_OPS TASKS_TRACING_OPS
+		TASKS_OPS TASKS_RUDE_OPS TASKS_TRACING_OPS LAZY_OPS
 		&trivial_ops,
 	};
 
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index cdbdd56e64b1..24ec925b2dfc 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -600,6 +600,7 @@ void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
 {
 	switch (test_type) {
 	case RCU_FLAVOR:
+	case RCU_LAZY_FLAVOR:
 		*flags = READ_ONCE(rcu_state.gp_flags);
 		*gp_seq = rcu_seq_current(&rcu_state.gp_seq);
 		break;
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/CFLIST b/tools/testing/selftests/rcutorture/configs/rcu/CFLIST
index 98b6175e5aa0..609c3370616f 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/CFLIST
+++ b/tools/testing/selftests/rcutorture/configs/rcu/CFLIST
@@ -5,6 +5,7 @@ TREE04
 TREE05
 TREE07
 TREE09
+TREE11
 SRCU-N
 SRCU-P
 SRCU-T
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE11 b/tools/testing/selftests/rcutorture/configs/rcu/TREE11
new file mode 100644
index 000000000000..436013f3e015
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE11
@@ -0,0 +1,18 @@
+CONFIG_SMP=y
+CONFIG_PREEMPT_NONE=n
+CONFIG_PREEMPT_VOLUNTARY=n
+CONFIG_PREEMPT=y
+#CHECK#CONFIG_PREEMPT_RCU=y
+CONFIG_HZ_PERIODIC=n
+CONFIG_NO_HZ_IDLE=y
+CONFIG_NO_HZ_FULL=n
+CONFIG_RCU_TRACE=y
+CONFIG_HOTPLUG_CPU=y
+CONFIG_MAXSMP=y
+CONFIG_CPUMASK_OFFSTACK=y
+CONFIG_RCU_NOCB_CPU=y
+CONFIG_DEBUG_LOCK_ALLOC=n
+CONFIG_RCU_BOOST=n
+CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
+CONFIG_RCU_EXPERT=y
+CONFIG_RCU_LAZY=y
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE11.boot b/tools/testing/selftests/rcutorture/configs/rcu/TREE11.boot
new file mode 100644
index 000000000000..9b6f720d4ccd
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE11.boot
@@ -0,0 +1,8 @@
+maxcpus=8 nr_cpus=43
+rcutree.gp_preinit_delay=3
+rcutree.gp_init_delay=3
+rcutree.gp_cleanup_delay=3
+rcu_nocbs=0-7
+rcutorture.torture_type=rcu_lazy
+rcutorture.nocbs_nthreads=8
+rcutorture.fwd_progress=0
-- 
2.37.0.144.g8ac04bfd2-goog

Re: [PATCH 1/5] rcu: Introduce call_rcu_lazy() API implementation

[Joel Fernandes]

On Wed, Jul 13, 2022 at 09:32:33PM +0000, Joel Fernandes (Google) wrote:

> + * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
> + * resulting RCU callback function "func()", then both CPU A and CPU B are
> + * guaranteed to execute a full memory barrier during the time interval
> + * between the call to call_rcu() and the invocation of "func()" -- even
> + * if CPU A and CPU B are the same CPU (but again only if the system has
> + * more than one CPU).
> + *
> + * Implementation of these memory-ordering guarantees is described here:
> + * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
> + */
> +void call_rcu(struct rcu_head *head, rcu_callback_t func)
> +{
> +	return __call_rcu_common(head, func, force_call_rcu_to_lazy);
> +
> +}

I will kill that extra new line. LOL something always has to go wrong no
matter how many hours you spend making sure eveyrthing is good :) Luckily
cosmetic here.

thanks,

 - Joel

Re: [PATCH v3 0/5] Implement call_rcu_lazy() and miscellaneous fixes

[Paul E. McKenney]

On Wed, Jul 13, 2022 at 09:32:32PM +0000, Joel Fernandes (Google) wrote:
> Hello!
> 
> Please find the next improved version of call_rcu_lazy() attached.  The main
> difference between the previous versions is that:
> - In v2 rcu_barrier is fixed to not hang (I found this to be due to a missing
>   GP thread wakeup), now I am limiting this wake up only to rcu_barrier() as
>   requested by Paul.
> - Fixed checkpatch and build robot issues.
> - Some more changes to 'lazy' parameter passing and consolidation of segcblist
>   functions.
> - more testing via rcutorture and rcuscale.

Thank you!  What I am going to do is to pull these into an experimental
not-for-mainline branch and run the usual set of rcutorture tests.
I will then take a look at the patches.

> Note that these tests were run on v2 patches, I am expecting similar power
> improvements however I've not yet tested power.
> 
> Following are power savings we saw on top of RCU_NOCB_CPU on an Intel platform
> in v2.  The observation is that due to a 'trickle down' effect of RCU
> callbacks, the system is very lightly loaded but constantly running few RCU
> callbacks very often. This confuses the power management hardware that the
> system is active, when it is in fact idle.
> 
> For example, when ChromeOS screen is off and user is not doing anything on the
> system, we can see big power savings.
> Before:
> Pk%pc10 = 72.13
> PkgWatt = 0.58
> CorWatt = 0.04
> 
> After:
> Pk%pc10 = 81.28
> PkgWatt = 0.41
> CorWatt = 0.03

When you update these numbers, please explain what they all are and
evaluate them in the cover letter (or in the relevant patch's commit log).
For final submission, please also include some estimate of the variance.
For example, CorWatt might be essentially the same both before and after,
as in 0.035 and 0.034, or there might be a large difference, as in 0.044
and 0.025.  The 81.28 might be constant in all four digits (ha!), or it
might vary between (say) 80 and 83.  And so on.

Based on our earlier emails, my guess is that Pk%pc10 is the percent of
time that the system is in a low-power state (bigger is better), PkgWatt
is power consumed by the CPU chip (smaller is better), and CorWatt is
power consumed by the CPU core (again, smaller is better).

It all might sound painfully obvious to you right now, but please have
pity on future readers of this series.

> Further, when ChromeOS screen is ON but system is idle or lightly loaded, we
> can see that the display pipeline is constantly doing RCU callback queuing due
> to open/close of file descriptors associated with graphics buffers. This is
> attributed to the file_free_rcu() path which this patch series also touches.
> 
> On memory pressure, timeout or queue growing too big, we initiate a flush of of
> the bypass lists holding the lazy CBs.
> 
> Similar results can be achieved by increasing jiffies_till_first_fqs, however
> that also has the effect of slowing down RCU. Especially I saw huge slow down

In the final submission, please quantify "huge slow down".  ;-)

> of function graph tracer when increasing that. That may be possible to fix via
> rcu_expedited=1 boot parameter, however call_rcu_lazy() provides another option
> over slowing down ALL call_rcu() globally. Further using jiffies_till_first_fqs
> approach will still cause a wake up of the main RCU GP kthread, with this work
> we delay even those wakeups.
> 
> One drawback of this series is, if another frequent RCU callback creeps up in
> the future, that's not lazy, then that will again hurt the power. However, I
> believe identifying and fixing those is a more reasonable approach than slowing
> RCU down for the whole system.

Like I said earlier, you are the official call_rcu_lazy() whack-a-mole
developer.  ;-)

							Thanx, Paul

> Disclaimer: I have intentionally not CC'd other subsystem maintainers (like
> net, fs) to keep noise low and will CC them in the future after 1 or 2 rounds
> of review and agreements.
> 
> Joel Fernandes (Google) (4):
>   rcu: Introduce call_rcu_lazy() API implementation
>   rcuscale: Add laziness and kfree tests
>   fs: Move call_rcu() to call_rcu_lazy() in some paths
>   rcutorture: Add test code for call_rcu_lazy()
> 
> Vineeth Pillai (1):
>   rcu: shrinker for lazy rcu
> 
>  fs/dcache.c                                   |   4 +-
>  fs/eventpoll.c                                |   2 +-
>  fs/file_table.c                               |   2 +-
>  fs/inode.c                                    |   2 +-
>  include/linux/rcu_segcblist.h                 |   1 +
>  include/linux/rcupdate.h                      |   6 +
>  kernel/rcu/Kconfig                            |   8 +
>  kernel/rcu/rcu.h                              |  12 +
>  kernel/rcu/rcu_segcblist.c                    |  15 +-
>  kernel/rcu/rcu_segcblist.h                    |  20 +-
>  kernel/rcu/rcuscale.c                         |  74 +++++-
>  kernel/rcu/rcutorture.c                       |  60 ++++-
>  kernel/rcu/tree.c                             | 132 ++++++----
>  kernel/rcu/tree.h                             |  10 +-
>  kernel/rcu/tree_nocb.h                        | 239 ++++++++++++++----
>  .../selftests/rcutorture/configs/rcu/TREE11   |  18 ++
>  .../rcutorture/configs/rcu/TREE11.boot        |   8 +
>  17 files changed, 508 insertions(+), 105 deletions(-)
>  create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/TREE11
>  create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/TREE11.boot
> 
> -- 
> 2.37.0.144.g8ac04bfd2-goog
> 

Re: [PATCH v3 0/5] Implement call_rcu_lazy() and miscellaneous fixes

[Joel Fernandes]

On 7/14/2022 4:51 PM, Paul E. McKenney wrote:
> On Wed, Jul 13, 2022 at 09:32:32PM +0000, Joel Fernandes (Google) wrote:
>> Hello!
>>
>> Please find the next improved version of call_rcu_lazy() attached.  The main
>> difference between the previous versions is that:
>> - In v2 rcu_barrier is fixed to not hang (I found this to be due to a missing
>>   GP thread wakeup), now I am limiting this wake up only to rcu_barrier() as
>>   requested by Paul.
>> - Fixed checkpatch and build robot issues.
>> - Some more changes to 'lazy' parameter passing and consolidation of segcblist
>>   functions.
>> - more testing via rcutorture and rcuscale.
> 
> Thank you!  What I am going to do is to pull these into an experimental
> not-for-mainline branch and run the usual set of rcutorture tests.
> I will then take a look at the patches.

Thanks, that sounds great.

> 
>> Note that these tests were run on v2 patches, I am expecting similar power
>> improvements however I've not yet tested power.
>>

>> Following are power savings we saw on top of RCU_NOCB_CPU on an Intel platform
>> in v2.  The observation is that due to a 'trickle down' effect of RCU
>> callbacks, the system is very lightly loaded but constantly running few RCU
>> callbacks very often. This confuses the power management hardware that the
>> system is active, when it is in fact idle.
>>
>> For example, when ChromeOS screen is off and user is not doing anything on the
>> system, we can see big power savings.
>> Before:
>> Pk%pc10 = 72.13
>> PkgWatt = 0.58
>> CorWatt = 0.04
>>
>> After:
>> Pk%pc10 = 81.28
>> PkgWatt = 0.41
>> CorWatt = 0.03
> 
> When you update these numbers, please explain what they all are and
> evaluate them in the cover letter (or in the relevant patch's commit log).
> For final submission, please also include some estimate of the variance.
> For example, CorWatt might be essentially the same both before and after,
> as in 0.035 and 0.034, or there might be a large difference, as in 0.044
> and 0.025.  The 81.28 might be constant in all four digits (ha!), or it
> might vary between (say) 80 and 83.  And so on.

Sure thanks for the suggestions and will do.

> 
> Based on our earlier emails, my guess is that Pk%pc10 is the percent of
> time that the system is in a low-power state (bigger is better), PkgWatt
> is power consumed by the CPU chip (smaller is better), and CorWatt is
> power consumed by the CPU core (again, smaller is better).

Yes that's correct.


>> Further, when ChromeOS screen is ON but system is idle or lightly loaded, we
>> can see that the display pipeline is constantly doing RCU callback queuing due
>> to open/close of file descriptors associated with graphics buffers. This is
>> attributed to the file_free_rcu() path which this patch series also touches.
>>
>> On memory pressure, timeout or queue growing too big, we initiate a flush of of
>> the bypass lists holding the lazy CBs.
>>
>> Similar results can be achieved by increasing jiffies_till_first_fqs, however
>> that also has the effect of slowing down RCU. Especially I saw huge slow down
> 
> In the final submission, please quantify "huge slow down".  ;-)

Sure will do. IIRC it was something like 30 second to stop function
graph tracer versus the usual 2-3 seconds.

>> of function graph tracer when increasing that. That may be possible to fix via
>> rcu_expedited=1 boot parameter, however call_rcu_lazy() provides another option
>> over slowing down ALL call_rcu() globally. Further using jiffies_till_first_fqs
>> approach will still cause a wake up of the main RCU GP kthread, with this work
>> we delay even those wakeups.
>>
>> One drawback of this series is, if another frequent RCU callback creeps up in
>> the future, that's not lazy, then that will again hurt the power. However, I
>> believe identifying and fixing those is a more reasonable approach than slowing
>> RCU down for the whole system.
> 
> Like I said earlier, you are the official call_rcu_lazy() whack-a-mole
> developer.  ;-)

Haha..

Thanks,

- Joel

Re: [PATCH v3 0/5] Implement call_rcu_lazy() and miscellaneous fixes

[Paul E. McKenney]

On Thu, Jul 14, 2022 at 01:51:54PM -0700, Paul E. McKenney wrote:
> On Wed, Jul 13, 2022 at 09:32:32PM +0000, Joel Fernandes (Google) wrote:
> > Hello!
> > 
> > Please find the next improved version of call_rcu_lazy() attached.  The main
> > difference between the previous versions is that:
> > - In v2 rcu_barrier is fixed to not hang (I found this to be due to a missing
> >   GP thread wakeup), now I am limiting this wake up only to rcu_barrier() as
> >   requested by Paul.
> > - Fixed checkpatch and build robot issues.
> > - Some more changes to 'lazy' parameter passing and consolidation of segcblist
> >   functions.
> > - more testing via rcutorture and rcuscale.
> 
> Thank you!  What I am going to do is to pull these into an experimental
> not-for-mainline branch and run the usual set of rcutorture tests.
> I will then take a look at the patches.

And there were a few conflicts with the nocb patch series in -rcu.
The allegedly conflict-resolved series is here: joel.2022.07.14a
Please let me know if I messed something up.

Again, this is an experimental series of commits for my testing.  And for
anyone else who would like to test against -rcu, for that matter.

						Thanx, Paul

> > Note that these tests were run on v2 patches, I am expecting similar power
> > improvements however I've not yet tested power.
> > 
> > Following are power savings we saw on top of RCU_NOCB_CPU on an Intel platform
> > in v2.  The observation is that due to a 'trickle down' effect of RCU
> > callbacks, the system is very lightly loaded but constantly running few RCU
> > callbacks very often. This confuses the power management hardware that the
> > system is active, when it is in fact idle.
> > 
> > For example, when ChromeOS screen is off and user is not doing anything on the
> > system, we can see big power savings.
> > Before:
> > Pk%pc10 = 72.13
> > PkgWatt = 0.58
> > CorWatt = 0.04
> > 
> > After:
> > Pk%pc10 = 81.28
> > PkgWatt = 0.41
> > CorWatt = 0.03
> 
> When you update these numbers, please explain what they all are and
> evaluate them in the cover letter (or in the relevant patch's commit log).
> For final submission, please also include some estimate of the variance.
> For example, CorWatt might be essentially the same both before and after,
> as in 0.035 and 0.034, or there might be a large difference, as in 0.044
> and 0.025.  The 81.28 might be constant in all four digits (ha!), or it
> might vary between (say) 80 and 83.  And so on.
> 
> Based on our earlier emails, my guess is that Pk%pc10 is the percent of
> time that the system is in a low-power state (bigger is better), PkgWatt
> is power consumed by the CPU chip (smaller is better), and CorWatt is
> power consumed by the CPU core (again, smaller is better).
> 
> It all might sound painfully obvious to you right now, but please have
> pity on future readers of this series.
> 
> > Further, when ChromeOS screen is ON but system is idle or lightly loaded, we
> > can see that the display pipeline is constantly doing RCU callback queuing due
> > to open/close of file descriptors associated with graphics buffers. This is
> > attributed to the file_free_rcu() path which this patch series also touches.
> > 
> > On memory pressure, timeout or queue growing too big, we initiate a flush of of
> > the bypass lists holding the lazy CBs.
> > 
> > Similar results can be achieved by increasing jiffies_till_first_fqs, however
> > that also has the effect of slowing down RCU. Especially I saw huge slow down
> 
> In the final submission, please quantify "huge slow down".  ;-)
> 
> > of function graph tracer when increasing that. That may be possible to fix via
> > rcu_expedited=1 boot parameter, however call_rcu_lazy() provides another option
> > over slowing down ALL call_rcu() globally. Further using jiffies_till_first_fqs
> > approach will still cause a wake up of the main RCU GP kthread, with this work
> > we delay even those wakeups.
> > 
> > One drawback of this series is, if another frequent RCU callback creeps up in
> > the future, that's not lazy, then that will again hurt the power. However, I
> > believe identifying and fixing those is a more reasonable approach than slowing
> > RCU down for the whole system.
> 
> Like I said earlier, you are the official call_rcu_lazy() whack-a-mole
> developer.  ;-)
> 
> 							Thanx, Paul
> 
> > Disclaimer: I have intentionally not CC'd other subsystem maintainers (like
> > net, fs) to keep noise low and will CC them in the future after 1 or 2 rounds
> > of review and agreements.
> > 
> > Joel Fernandes (Google) (4):
> >   rcu: Introduce call_rcu_lazy() API implementation
> >   rcuscale: Add laziness and kfree tests
> >   fs: Move call_rcu() to call_rcu_lazy() in some paths
> >   rcutorture: Add test code for call_rcu_lazy()
> > 
> > Vineeth Pillai (1):
> >   rcu: shrinker for lazy rcu
> > 
> >  fs/dcache.c                                   |   4 +-
> >  fs/eventpoll.c                                |   2 +-
> >  fs/file_table.c                               |   2 +-
> >  fs/inode.c                                    |   2 +-
> >  include/linux/rcu_segcblist.h                 |   1 +
> >  include/linux/rcupdate.h                      |   6 +
> >  kernel/rcu/Kconfig                            |   8 +
> >  kernel/rcu/rcu.h                              |  12 +
> >  kernel/rcu/rcu_segcblist.c                    |  15 +-
> >  kernel/rcu/rcu_segcblist.h                    |  20 +-
> >  kernel/rcu/rcuscale.c                         |  74 +++++-
> >  kernel/rcu/rcutorture.c                       |  60 ++++-
> >  kernel/rcu/tree.c                             | 132 ++++++----
> >  kernel/rcu/tree.h                             |  10 +-
> >  kernel/rcu/tree_nocb.h                        | 239 ++++++++++++++----
> >  .../selftests/rcutorture/configs/rcu/TREE11   |  18 ++
> >  .../rcutorture/configs/rcu/TREE11.boot        |   8 +
> >  17 files changed, 508 insertions(+), 105 deletions(-)
> >  create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/TREE11
> >  create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/TREE11.boot
> > 
> > -- 
> > 2.37.0.144.g8ac04bfd2-goog
> > 

Re: [PATCH v3 0/5] Implement call_rcu_lazy() and miscellaneous fixes

[Joel Fernandes]

On Thu, Jul 14, 2022 at 03:21:31PM -0700, Paul E. McKenney wrote:
> On Thu, Jul 14, 2022 at 01:51:54PM -0700, Paul E. McKenney wrote:
> > On Wed, Jul 13, 2022 at 09:32:32PM +0000, Joel Fernandes (Google) wrote:
> > > Hello!
> > > 
> > > Please find the next improved version of call_rcu_lazy() attached.  The main
> > > difference between the previous versions is that:
> > > - In v2 rcu_barrier is fixed to not hang (I found this to be due to a missing
> > >   GP thread wakeup), now I am limiting this wake up only to rcu_barrier() as
> > >   requested by Paul.
> > > - Fixed checkpatch and build robot issues.
> > > - Some more changes to 'lazy' parameter passing and consolidation of segcblist
> > >   functions.
> > > - more testing via rcutorture and rcuscale.
> > 
> > Thank you!  What I am going to do is to pull these into an experimental
> > not-for-mainline branch and run the usual set of rcutorture tests.
> > I will then take a look at the patches.
> 
> And there were a few conflicts with the nocb patch series in -rcu.
> The allegedly conflict-resolved series is here: joel.2022.07.14a
> Please let me know if I messed something up.

Thanks, it looks Ok. There is one robot fix for hexagon's arch where I think
TREE_RCU is disabled, could you apply the diff below to patch 1/5 ?

Or, I can also just keep it in my version of 1/5 to go out with the next rev.

---8<-----------------------

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index c358387fd223..aa3243e49506 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -464,6 +464,14 @@ enum rcutorture_type {
 	INVALID_RCU_FLAVOR
 };
 
+#if defined(CONFIG_RCU_LAZY)
+unsigned long rcu_lazy_get_jiffies_till_flush(void);
+void rcu_lazy_set_jiffies_till_flush(unsigned long j);
+#else
+static inline unsigned long rcu_lazy_get_jiffies_till_flush(void) { return 0; }
+static inline void rcu_lazy_set_jiffies_till_flush(unsigned long j) { }
+#endif
+
 #if defined(CONFIG_TREE_RCU)
 void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
 			    unsigned long *gp_seq);
@@ -475,14 +483,6 @@ void do_trace_rcu_torture_read(const char *rcutorturename,
 void rcu_gp_set_torture_wait(int duration);
 void rcu_force_call_rcu_to_lazy(bool force);
 
-#if defined(CONFIG_RCU_LAZY)
-unsigned long rcu_lazy_get_jiffies_till_flush(void);
-void rcu_lazy_set_jiffies_till_flush(unsigned long j);
-#else
-static inline unsigned long rcu_lazy_get_jiffies_till_flush(void) { return 0; }
-static inline void rcu_lazy_set_jiffies_till_flush(unsigned long j) { }
-#endif
-
 #else
 static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
 					  int *flags, unsigned long *gp_seq)

Re: [PATCH v3 0/5] Implement call_rcu_lazy() and miscellaneous fixes

[Paul E. McKenney]

On Fri, Jul 15, 2022 at 03:18:04PM +0000, Joel Fernandes wrote:
> On Thu, Jul 14, 2022 at 03:21:31PM -0700, Paul E. McKenney wrote:
> > On Thu, Jul 14, 2022 at 01:51:54PM -0700, Paul E. McKenney wrote:
> > > On Wed, Jul 13, 2022 at 09:32:32PM +0000, Joel Fernandes (Google) wrote:
> > > > Hello!
> > > > 
> > > > Please find the next improved version of call_rcu_lazy() attached.  The main
> > > > difference between the previous versions is that:
> > > > - In v2 rcu_barrier is fixed to not hang (I found this to be due to a missing
> > > >   GP thread wakeup), now I am limiting this wake up only to rcu_barrier() as
> > > >   requested by Paul.
> > > > - Fixed checkpatch and build robot issues.
> > > > - Some more changes to 'lazy' parameter passing and consolidation of segcblist
> > > >   functions.
> > > > - more testing via rcutorture and rcuscale.
> > > 
> > > Thank you!  What I am going to do is to pull these into an experimental
> > > not-for-mainline branch and run the usual set of rcutorture tests.
> > > I will then take a look at the patches.
> > 
> > And there were a few conflicts with the nocb patch series in -rcu.
> > The allegedly conflict-resolved series is here: joel.2022.07.14a
> > Please let me know if I messed something up.
> 
> Thanks, it looks Ok. There is one robot fix for hexagon's arch where I think
> TREE_RCU is disabled, could you apply the diff below to patch 1/5 ?
> 
> Or, I can also just keep it in my version of 1/5 to go out with the next rev.

Given that I am not testing on hexagon, I will let you fix this one on
the next rev.  If someone out there is testing this branch on hexagon,
they should feel free to apply your patch locally.  ;-)

							Thanx, Paul

> ---8<-----------------------
> 
> diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
> index c358387fd223..aa3243e49506 100644
> --- a/kernel/rcu/rcu.h
> +++ b/kernel/rcu/rcu.h
> @@ -464,6 +464,14 @@ enum rcutorture_type {
>  	INVALID_RCU_FLAVOR
>  };
>  
> +#if defined(CONFIG_RCU_LAZY)
> +unsigned long rcu_lazy_get_jiffies_till_flush(void);
> +void rcu_lazy_set_jiffies_till_flush(unsigned long j);
> +#else
> +static inline unsigned long rcu_lazy_get_jiffies_till_flush(void) { return 0; }
> +static inline void rcu_lazy_set_jiffies_till_flush(unsigned long j) { }
> +#endif
> +
>  #if defined(CONFIG_TREE_RCU)
>  void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
>  			    unsigned long *gp_seq);
> @@ -475,14 +483,6 @@ void do_trace_rcu_torture_read(const char *rcutorturename,
>  void rcu_gp_set_torture_wait(int duration);
>  void rcu_force_call_rcu_to_lazy(bool force);
>  
> -#if defined(CONFIG_RCU_LAZY)
> -unsigned long rcu_lazy_get_jiffies_till_flush(void);
> -void rcu_lazy_set_jiffies_till_flush(unsigned long j);
> -#else
> -static inline unsigned long rcu_lazy_get_jiffies_till_flush(void) { return 0; }
> -static inline void rcu_lazy_set_jiffies_till_flush(unsigned long j) { }
> -#endif
> -
>  #else
>  static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
>  					  int *flags, unsigned long *gp_seq)

Re: [PATCH v3 0/5] Implement call_rcu_lazy() and miscellaneous fixes

[Joel Fernandes]

On Fri, Jul 15, 2022 at 08:29:37AM -0700, Paul E. McKenney wrote:
> On Fri, Jul 15, 2022 at 03:18:04PM +0000, Joel Fernandes wrote:
> > On Thu, Jul 14, 2022 at 03:21:31PM -0700, Paul E. McKenney wrote:
> > > On Thu, Jul 14, 2022 at 01:51:54PM -0700, Paul E. McKenney wrote:
> > > > On Wed, Jul 13, 2022 at 09:32:32PM +0000, Joel Fernandes (Google) wrote:
> > > > > Hello!
> > > > > 
> > > > > Please find the next improved version of call_rcu_lazy() attached.  The main
> > > > > difference between the previous versions is that:
> > > > > - In v2 rcu_barrier is fixed to not hang (I found this to be due to a missing
> > > > >   GP thread wakeup), now I am limiting this wake up only to rcu_barrier() as
> > > > >   requested by Paul.
> > > > > - Fixed checkpatch and build robot issues.
> > > > > - Some more changes to 'lazy' parameter passing and consolidation of segcblist
> > > > >   functions.
> > > > > - more testing via rcutorture and rcuscale.
> > > > 
> > > > Thank you!  What I am going to do is to pull these into an experimental
> > > > not-for-mainline branch and run the usual set of rcutorture tests.
> > > > I will then take a look at the patches.
> > > 
> > > And there were a few conflicts with the nocb patch series in -rcu.
> > > The allegedly conflict-resolved series is here: joel.2022.07.14a
> > > Please let me know if I messed something up.
> > 
> > Thanks, it looks Ok. There is one robot fix for hexagon's arch where I think
> > TREE_RCU is disabled, could you apply the diff below to patch 1/5 ?
> > 
> > Or, I can also just keep it in my version of 1/5 to go out with the next rev.
> 
> Given that I am not testing on hexagon, I will let you fix this one on
> the next rev.  If someone out there is testing this branch on hexagon,
> they should feel free to apply your patch locally.  ;-)

I am pretty sure this is the feature that was going to make Hexagon widely
adopted, but your call ;-)

thanks,

 - Joel

Re: [PATCH v3 0/5] Implement call_rcu_lazy() and miscellaneous fixes

[Joel Fernandes]

On Fri, Jul 15, 2022 at 03:40:33PM +0000, Joel Fernandes wrote:
> On Fri, Jul 15, 2022 at 08:29:37AM -0700, Paul E. McKenney wrote:
> > On Fri, Jul 15, 2022 at 03:18:04PM +0000, Joel Fernandes wrote:
> > > On Thu, Jul 14, 2022 at 03:21:31PM -0700, Paul E. McKenney wrote:
> > > > On Thu, Jul 14, 2022 at 01:51:54PM -0700, Paul E. McKenney wrote:
> > > > > On Wed, Jul 13, 2022 at 09:32:32PM +0000, Joel Fernandes (Google) wrote:
> > > > > > Hello!
> > > > > > 
> > > > > > Please find the next improved version of call_rcu_lazy() attached.  The main
> > > > > > difference between the previous versions is that:
> > > > > > - In v2 rcu_barrier is fixed to not hang (I found this to be due to a missing
> > > > > >   GP thread wakeup), now I am limiting this wake up only to rcu_barrier() as
> > > > > >   requested by Paul.
> > > > > > - Fixed checkpatch and build robot issues.
> > > > > > - Some more changes to 'lazy' parameter passing and consolidation of segcblist
> > > > > >   functions.
> > > > > > - more testing via rcutorture and rcuscale.
> > > > > 
> > > > > Thank you!  What I am going to do is to pull these into an experimental
> > > > > not-for-mainline branch and run the usual set of rcutorture tests.
> > > > > I will then take a look at the patches.
> > > > 
> > > > And there were a few conflicts with the nocb patch series in -rcu.
> > > > The allegedly conflict-resolved series is here: joel.2022.07.14a
> > > > Please let me know if I messed something up.
> > > 
> > > Thanks, it looks Ok. There is one robot fix for hexagon's arch where I think
> > > TREE_RCU is disabled, could you apply the diff below to patch 1/5 ?
> > > 
> > > Or, I can also just keep it in my version of 1/5 to go out with the next rev.
> > 
> > Given that I am not testing on hexagon, I will let you fix this one on
> > the next rev.  If someone out there is testing this branch on hexagon,
> > they should feel free to apply your patch locally.  ;-)
> 
> I am pretty sure this is the feature that was going to make Hexagon widely
> adopted, but your call ;-)

Jokes apart, I am sure this feature will be useful to a lot of folks and
architectures but lets keep this diff for the next revision as you said.

Actually never heard of Hexagon till today... 32-bit and 4x VLIW, Cool! :
https://en.wikipedia.org/wiki/Qualcomm_Hexagon

thanks,

 - Joel

Re: [PATCH v3 0/5] Implement call_rcu_lazy() and miscellaneous fixes

[Paul E. McKenney]

On Fri, Jul 15, 2022 at 03:50:17PM +0000, Joel Fernandes wrote:
> On Fri, Jul 15, 2022 at 03:40:33PM +0000, Joel Fernandes wrote:
> > On Fri, Jul 15, 2022 at 08:29:37AM -0700, Paul E. McKenney wrote:
> > > On Fri, Jul 15, 2022 at 03:18:04PM +0000, Joel Fernandes wrote:
> > > > On Thu, Jul 14, 2022 at 03:21:31PM -0700, Paul E. McKenney wrote:
> > > > > On Thu, Jul 14, 2022 at 01:51:54PM -0700, Paul E. McKenney wrote:
> > > > > > On Wed, Jul 13, 2022 at 09:32:32PM +0000, Joel Fernandes (Google) wrote:
> > > > > > > Hello!
> > > > > > > 
> > > > > > > Please find the next improved version of call_rcu_lazy() attached.  The main
> > > > > > > difference between the previous versions is that:
> > > > > > > - In v2 rcu_barrier is fixed to not hang (I found this to be due to a missing
> > > > > > >   GP thread wakeup), now I am limiting this wake up only to rcu_barrier() as
> > > > > > >   requested by Paul.
> > > > > > > - Fixed checkpatch and build robot issues.
> > > > > > > - Some more changes to 'lazy' parameter passing and consolidation of segcblist
> > > > > > >   functions.
> > > > > > > - more testing via rcutorture and rcuscale.
> > > > > > 
> > > > > > Thank you!  What I am going to do is to pull these into an experimental
> > > > > > not-for-mainline branch and run the usual set of rcutorture tests.
> > > > > > I will then take a look at the patches.
> > > > > 
> > > > > And there were a few conflicts with the nocb patch series in -rcu.
> > > > > The allegedly conflict-resolved series is here: joel.2022.07.14a
> > > > > Please let me know if I messed something up.
> > > > 
> > > > Thanks, it looks Ok. There is one robot fix for hexagon's arch where I think
> > > > TREE_RCU is disabled, could you apply the diff below to patch 1/5 ?
> > > > 
> > > > Or, I can also just keep it in my version of 1/5 to go out with the next rev.
> > > 
> > > Given that I am not testing on hexagon, I will let you fix this one on
> > > the next rev.  If someone out there is testing this branch on hexagon,
> > > they should feel free to apply your patch locally.  ;-)
> > 
> > I am pretty sure this is the feature that was going to make Hexagon widely
> > adopted, but your call ;-)

Then they should be highly motivated to apply your patch.  ;-)

> Jokes apart, I am sure this feature will be useful to a lot of folks and
> architectures but lets keep this diff for the next revision as you said.
> 
> Actually never heard of Hexagon till today... 32-bit and 4x VLIW, Cool! :
> https://en.wikipedia.org/wiki/Qualcomm_Hexagon

Indeed, there are still about 20 different types of processors running Linux.

							Thanx, Paul

Re: [PATCH v3 0/5] Implement call_rcu_lazy() and miscellaneous fixes

[Joel Fernandes]

On 7/14/2022 4:51 PM, Paul E. McKenney wrote:
> On Wed, Jul 13, 2022 at 09:32:32PM +0000, Joel Fernandes (Google) wrote:
>> Hello!
>>
>> Please find the next improved version of call_rcu_lazy() attached.  The main
>> difference between the previous versions is that:
>> - In v2 rcu_barrier is fixed to not hang (I found this to be due to a missing
>>   GP thread wakeup), now I am limiting this wake up only to rcu_barrier() as
>>   requested by Paul.
>> - Fixed checkpatch and build robot issues.
>> - Some more changes to 'lazy' parameter passing and consolidation of segcblist
>>   functions.
>> - more testing via rcutorture and rcuscale.
> 
> Thank you!  What I am going to do is to pull these into an experimental
> not-for-mainline branch and run the usual set of rcutorture tests.
> I will then take a look at the patches.
> 
>> Note that these tests were run on v2 patches, I am expecting similar power
>> improvements however I've not yet tested power.
>>
>> Following are power savings we saw on top of RCU_NOCB_CPU on an Intel platform
>> in v2.  The observation is that due to a 'trickle down' effect of RCU
>> callbacks, the system is very lightly loaded but constantly running few RCU
>> callbacks very often. This confuses the power management hardware that the
>> system is active, when it is in fact idle.
>>
>> For example, when ChromeOS screen is off and user is not doing anything on the
>> system, we can see big power savings.
>> Before:
>> Pk%pc10 = 72.13
>> PkgWatt = 0.58
>> CorWatt = 0.04
>>
>> After:
>> Pk%pc10 = 81.28
>> PkgWatt = 0.41
>> CorWatt = 0.03
> 
> When you update these numbers, please explain what they all are and
> evaluate them in the cover letter (or in the relevant patch's commit log).
> For final submission, please also include some estimate of the variance.
> For example, CorWatt might be essentially the same both before and after,
> as in 0.035 and 0.034, or there might be a large difference, as in 0.044
> and 0.025.  The 81.28 might be constant in all four digits (ha!), or it
> might vary between (say) 80 and 83.  And so on.
> 
> Based on our earlier emails, my guess is that Pk%pc10 is the percent of
> time that the system is in a low-power state (bigger is better), PkgWatt
> is power consumed by the CPU chip (smaller is better), and CorWatt is
> power consumed by the CPU core (again, smaller is better).
> 
> It all might sound painfully obvious to you right now, but please have
> pity on future readers of this series.

Following is some power data I collected with Turbostat on an x86 ChromeOS
ADL machine. The power seems better on the upstream kernel already versus
my earlier tests, however I still see 5-8% power improvement with the patches.

Rushikesh, Sitanshu, Neeraj, Vlad - could you test power with these as well?
The following branch boots on ChromeOS ADL:
https://github.com/joelagnel/linux-kernel/tree/chromeos-kernelupstream-5.19-rc4.aug22

These are output from Turbostat running:
turbostat -S -s PkgWatt,CorWatt --interval 5
PkgWatt - summary of package power in Watts 5 second interval.
CoreWatt - summary of core power in Watts 5 second interval.

I could not get PC10% on the upstream kernel, it always shows 0. Maybe that is a turbostat
version issue or something.

+───────────+─────────────────────────+──────────+───+──────────────────────────+──────────+
|           | Screen on idle (After)  |          |   | Screen on idle (Before)  |          |
+───────────+─────────────────────────+──────────+───+──────────────────────────+──────────+
|           | PkgWatt                 | CorWatt  |   | PkgWatt                  | CorWatt  |
|           |                         |          |   |                          |          |
|           | 0.6100                  | 0.0500   |   | 0.6700                   | 0.0500   |
|           | 0.5800                  | 0.0400   |   | 0.6200                   | 0.0500   |
|           | 0.5800                  | 0.0400   |   | 0.6500                   | 0.0500   |
|           | 0.6600                  | 0.0800   |   | 0.6200                   | 0.0500   |
|           | 0.5900                  | 0.0400   |   | 0.6200                   | 0.0500   |
|           | 0.5900                  | 0.0400   |   | 0.6400                   | 0.0600   |
|           | 0.6000                  | 0.0500   |   | 0.6700                   | 0.0600   |
|           | 0.6400                  | 0.0600   |   | 0.6200                   | 0.0500   |
|           | 0.6000                  | 0.0500   |   | 0.6200                   | 0.0500   |
|           | 0.5800                  | 0.0400   |   | 0.6200                   | 0.0500   |
|           | 0.6000                  | 0.0400   |   | 0.6200                   | 0.0500   |
|           | 0.6000                  | 0.0500   |   | 0.7200                   | 0.0900   |
--------------------------------------------------------------------------------------------
| Variance  | 0.0006                  | 0.0001   |   | 0.0010                   | 0.0001   |
| Mean      | 0.6025                  | 0.0483   |   | 0.6408                   | 0.0550   |
--------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------
|           | Lid closed + no suspend            |   Lid closed + no suspend               |
|                                                |                                         |
|           | Screen off idle (After)            |   | Screen off idle (Before)            |
--------------------------------------------------------------------------------------------
|           | PkgWatt                 | CorWatt  |   | PkgWatt                  | CorWatt  |
|           | 0.3100                  | 0.0700   |   | 0.3500                   | 0.0700   |
|           | 0.3100                  | 0.0700   |   | 0.3200                   | 0.0700   |
|           | 0.3300                  | 0.0700   |   | 0.4100                   | 0.0900   |
|           | 0.3100                  | 0.0600   |   | 0.3400                   | 0.0700   |
|           | 0.3300                  | 0.0700   |   | 0.3200                   | 0.0700   |
|           | 0.3800                  | 0.0900   |   | 0.3400                   | 0.0700   |
|           | 0.3600                  | 0.0700   |   | 0.3400                   | 0.0700   |
|           | 0.3100                  | 0.0700   |   | 0.3300                   | 0.0700   |
|           | 0.3300                  | 0.0700   |   | 0.3300                   | 0.0800   |
|           | 0.3700                  | 0.0800   |   | 0.3200                   | 0.0700   |
|           | 0.3500                  | 0.0800   |   | 0.3400                   | 0.0700   |
|           | 0.2900                  | 0.0600   |   | 0.4300                   | 0.1100   |
|           | 0.3300                  | 0.0700   |   | 0.3400                   | 0.0700   |
|           | 0.3300                  | 0.0700   |   | 0.3200                   | 0.0700   |
|           | 0.3400                  | 0.0700   |   | 0.3600                   | 0.0800   |
|           | 0.3000                  | 0.0700   |   | 0.3200                   | 0.0700   |
|           | 0.3400                  | 0.0700   |   | 0.3300                   | 0.0700   |
|           | 0.3400                  | 0.0900   |   | 0.3500                   | 0.0800   |
|           | 0.3400                  | 0.0700   |   | 0.3800                   | 0.0800   |
--------------------------------------------------------------------------------------------
| Variance  | 0.0005                  | 0.0001   |   | 0.0010                   | 0.0001   |
| Mean      | 0.3028                  | 0.0664   |   | 0.3174                   | 0.0700   |
+───────────+─────────────────────────+──────────+───+──────────────────────────+──────────+

Thanks,

 - Joel