[PATCH tip/core/rcu 2/8] rcu: Rename rcu_check_callbacks() to rcu_sched_clock_irq()

From: Paul E. McKenney
Date: Wed Jan 09 2019 - 16:42:04 EST

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The name rcu_check_callbacks() arguably made sense back in the early
2000s when RCU was quite a bit simpler than it is today, but it has
become quite misleading, especially with the advent of dyntick-idle
and NO_HZ_FULL. The rcu_check_callbacks() function is RCU's hook into
the scheduling-clock interrupt, and is now but one of many ways that
callbacks get promoted to invocable state.

This commit therefore changes the name to rcu_sched_clock_irq(),
which is the same number of characters and clearly indicates this
function's relation to the rest of the Linux kernel. In addition, for
the sake of consistency, rcu_flavor_check_callbacks() is also renamed
to rcu_flavor_sched_clock_irq().

While in the area, the header comments for both functions are reworked.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx>
---
.../Tree-RCU-Memory-Ordering.html | 4 ++--
.../TreeRCU-callback-invocation.svg | 2 +-
.../RCU/Design/Memory-Ordering/TreeRCU-gp.svg | 4 ++--
.../RCU/Design/Memory-Ordering/TreeRCU-qs.svg | 2 +-
include/linux/rcupdate.h | 2 +-
kernel/rcu/tiny.c | 2 +-
kernel/rcu/tree.c | 18 +++++++-------
kernel/rcu/tree.h | 2 +-
kernel/rcu/tree_plugin.h | 24 ++++++++-----------
kernel/time/timer.c | 2 +-
10 files changed, 29 insertions(+), 33 deletions(-)

diff --git a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html
index e4d94fba6c89..a3acfd49255f 100644
--- a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html
+++ b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html
@@ -485,7 +485,7 @@ section that the grace period must wait on.
noted by <tt>rcu_node_context_switch()</tt> on the left.
On the other hand, if the CPU takes a scheduler-clock interrupt
while executing in usermode, a quiescent state will be noted by
-<tt>rcu_check_callbacks()</tt> on the right.
+<tt>rcu_sched_clock_irq()</tt> on the right.
Either way, the passage through a quiescent state will be noted
in a per-CPU variable.

@@ -651,7 +651,7 @@ to end.
These callbacks are identified by <tt>rcu_advance_cbs()</tt>,
which is usually invoked by <tt>__note_gp_changes()</tt>.
As shown in the diagram below, this invocation can be triggered by
-the scheduling-clock interrupt (<tt>rcu_check_callbacks()</tt> on
+the scheduling-clock interrupt (<tt>rcu_sched_clock_irq()</tt> on
the left) or by idle entry (<tt>rcu_cleanup_after_idle()</tt> on
the right, but only for kernels build with
<tt>CONFIG_RCU_FAST_NO_HZ=y</tt>).
diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-callback-invocation.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-callback-invocation.svg
index 832408313d93..3fcf0c17cef2 100644
--- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-callback-invocation.svg
+++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-callback-invocation.svg
@@ -349,7 +349,7 @@
font-weight="bold"
font-size="192"
id="text202-7-5"
- style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_check_callbacks()</text>
+ style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_sched_clock_irq()</text>
<rect
x="7069.6187"
y="5087.4678"
diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg
index acd73c7ad0f4..f0bbe6f8d729 100644
--- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg
+++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg
@@ -3902,7 +3902,7 @@
font-style="normal"
y="-4418.6582"
x="3745.7725"
- xml:space="preserve">rcu_check_callbacks()</text>
+ xml:space="preserve">rcu_sched_clock_irq()</text>
</g>
<g
transform="translate(-850.30204,55463.106)"
@@ -4968,7 +4968,7 @@
font-weight="bold"
font-size="192"
id="text202-7-5-19"
- style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_check_callbacks()</text>
+ style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_sched_clock_irq()</text>
<rect
x="5314.2671"
y="82817.688"
diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-qs.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-qs.svg
index 149bec2a4493..3596ffdd4685 100644
--- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-qs.svg
+++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-qs.svg
@@ -775,7 +775,7 @@
font-style="normal"
y="-4418.6582"
x="3745.7725"
- xml:space="preserve">rcu_check_callbacks()</text>
+ xml:space="preserve">rcu_sched_clock_irq()</text>
</g>
<g
transform="translate(399.7744,828.86448)"
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index d8a8302e21f0..b4e99639d6d4 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -89,7 +89,7 @@ static inline int rcu_preempt_depth(void)
/* Internal to kernel */
void rcu_init(void);
extern int rcu_scheduler_active __read_mostly;
-void rcu_check_callbacks(int user);
+void rcu_sched_clock_irq(int user);
void rcu_report_dead(unsigned int cpu);
void rcutree_migrate_callbacks(int cpu);

diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index 5f5963ba313e..d7a9135b9471 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -76,7 +76,7 @@ void rcu_qs(void)
* be called from hardirq context. It is normally called from the
* scheduling-clock interrupt.
*/
-void rcu_check_callbacks(int user)
+void rcu_sched_clock_irq(int user)
{
if (user) {
rcu_qs();
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 9180158756d2..a79dd51c9cce 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1115,7 +1115,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
}

/*
- * NO_HZ_FULL CPUs can run in-kernel without rcu_check_callbacks!
+ * NO_HZ_FULL CPUs can run in-kernel without rcu_sched_clock_irq!
* The above code handles this, but only for straight cond_resched().
* And some in-kernel loops check need_resched() before calling
* cond_resched(), which defeats the above code for CPUs that are
@@ -2497,14 +2497,14 @@ static void rcu_do_batch(struct rcu_data *rdp)
}

/*
- * Check to see if this CPU is in a non-context-switch quiescent state
- * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
- * Also schedule RCU core processing.
- *
- * This function must be called from hardirq context. It is normally
- * invoked from the scheduling-clock interrupt.
+ * This function is invoked from each scheduling-clock interrupt,
+ * and checks to see if this CPU is in a non-context-switch quiescent
+ * state, for example, user mode or idle loop. It also schedules RCU
+ * core processing. If the current grace period has gone on too long,
+ * it will ask the scheduler to manufacture a context switch for the sole
+ * purpose of providing a providing the needed quiescent state.
*/
-void rcu_check_callbacks(int user)
+void rcu_sched_clock_irq(int user)
{
trace_rcu_utilization(TPS("Start scheduler-tick"));
raw_cpu_inc(rcu_data.ticks_this_gp);
@@ -2517,7 +2517,7 @@ void rcu_check_callbacks(int user)
}
__this_cpu_write(rcu_data.rcu_urgent_qs, false);
}
- rcu_flavor_check_callbacks(user);
+ rcu_flavor_sched_clock_irq(user);
if (rcu_pending())
invoke_rcu_core();

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index d90b02b53c0e..6562411de80d 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -420,7 +420,7 @@ static void rcu_print_detail_task_stall(void);
static int rcu_print_task_stall(struct rcu_node *rnp);
static int rcu_print_task_exp_stall(struct rcu_node *rnp);
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
-static void rcu_flavor_check_callbacks(int user);
+static void rcu_flavor_sched_clock_irq(int user);
void call_rcu(struct rcu_head *head, rcu_callback_t func);
static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck);
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 1b3dd2fc0cd6..575671646c60 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -307,7 +307,7 @@ static void rcu_qs(void)
__this_cpu_read(rcu_data.gp_seq),
TPS("cpuqs"));
__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
- barrier(); /* Coordinate with rcu_flavor_check_callbacks(). */
+ barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
current->rcu_read_unlock_special.b.need_qs = false;
}
}
@@ -788,13 +788,13 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
}

/*
- * Check for a quiescent state from the current CPU. When a task blocks,
- * the task is recorded in the corresponding CPU's rcu_node structure,
- * which is checked elsewhere.
- *
- * Caller must disable hard irqs.
+ * Check for a quiescent state from the current CPU, including voluntary
+ * context switches for Tasks RCU. When a task blocks, the task is
+ * recorded in the corresponding CPU's rcu_node structure, which is checked
+ * elsewhere, hence this function need only check for quiescent states
+ * related to the current CPU, not to those related to tasks.
*/
-static void rcu_flavor_check_callbacks(int user)
+static void rcu_flavor_sched_clock_irq(int user)
{
struct task_struct *t = current;

@@ -1088,14 +1088,10 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
}

/*
- * Check to see if this CPU is in a non-context-switch quiescent state
- * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
- * Also schedule RCU core processing.
- *
- * This function must be called from hardirq context. It is normally
- * invoked from the scheduling-clock interrupt.
+ * Check to see if this CPU is in a non-context-switch quiescent state,
+ * namely user mode and idle loop.
*/
-static void rcu_flavor_check_callbacks(int user)
+static void rcu_flavor_sched_clock_irq(int user)
{
if (user || rcu_is_cpu_rrupt_from_idle()) {

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 444156debfa0..6eb7cc4b6d52 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1632,7 +1632,7 @@ void update_process_times(int user_tick)
/* Note: this timer irq context must be accounted for as well. */
account_process_tick(p, user_tick);
run_local_timers();
- rcu_check_callbacks(user_tick);
+ rcu_sched_clock_irq(user_tick);
#ifdef CONFIG_IRQ_WORK
if (in_irq())
irq_work_tick();
--
2.17.1

Next message: Paul E. McKenney: "[PATCH tip/core/rcu 8/8] time: Move CONTEXT_TRACKING to kernel/time/Kconfig"
Previous message: Paul E. McKenney: "[PATCH tip/core/rcu 7/8] rcu: Add sparse check to rcu_assign_pointer()"
In reply to: Paul E. McKenney: "[PATCH tip/core/rcu 7/8] rcu: Add sparse check to rcu_assign_pointer()"
Next in thread: Paul E. McKenney: "[PATCH tip/core/rcu 8/8] time: Move CONTEXT_TRACKING to kernel/time/Kconfig"
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