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Date: Fri, 15 Aug 2014 09:28:45 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
bobby.prani@...il.com,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH v6 tip/core/rcu 17/17] rcu: Per-CPU operation cleanups to rcu_*_qs() functions
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
The rcu_bh_qs(), rcu_preempt_qs(), and rcu_sched_qs() functions use
old-style per-CPU variable access and write to ->passed_quiesce even
if it is already set. This commit therefore updates to use the new-style
per-CPU variable access functions and avoids the spurious writes.
This commit also eliminates the "cpu" argument to these functions because
they are always invoked on the indicated CPU.
Reported-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
include/linux/rcupdate.h | 4 ++--
include/linux/rcutiny.h | 2 +-
kernel/rcu/tiny.c | 10 +++++-----
kernel/rcu/tree.c | 34 ++++++++++++++++++----------------
kernel/rcu/tree_plugin.h | 27 +++++++++++++++------------
kernel/softirq.c | 2 +-
6 files changed, 42 insertions(+), 37 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index cc6858666b6d..160bc1718070 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -261,8 +261,8 @@ static inline int rcu_preempt_depth(void)
/* Internal to kernel */
void rcu_init(void);
-void rcu_sched_qs(int cpu);
-void rcu_bh_qs(int cpu);
+void rcu_sched_qs(void);
+void rcu_bh_qs(void);
void rcu_check_callbacks(int cpu, int user);
struct notifier_block;
void rcu_idle_enter(void);
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index d40a6a451330..38cc5b1e252d 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -80,7 +80,7 @@ static inline void kfree_call_rcu(struct rcu_head *head,
static inline void rcu_note_context_switch(int cpu)
{
- rcu_sched_qs(cpu);
+ rcu_sched_qs();
}
/*
diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index 717f00854fc0..61b8d2ccc2cb 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -72,7 +72,7 @@ static void rcu_idle_enter_common(long long newval)
current->pid, current->comm,
idle->pid, idle->comm); /* must be idle task! */
}
- rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
+ rcu_sched_qs(); /* implies rcu_bh_inc() */
barrier();
rcu_dynticks_nesting = newval;
}
@@ -217,7 +217,7 @@ static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
* are at it, given that any rcu quiescent state is also an rcu_bh
* quiescent state. Use "+" instead of "||" to defeat short circuiting.
*/
-void rcu_sched_qs(int cpu)
+void rcu_sched_qs(void)
{
unsigned long flags;
@@ -231,7 +231,7 @@ void rcu_sched_qs(int cpu)
/*
* Record an rcu_bh quiescent state.
*/
-void rcu_bh_qs(int cpu)
+void rcu_bh_qs(void)
{
unsigned long flags;
@@ -251,9 +251,9 @@ void rcu_check_callbacks(int cpu, int user)
{
RCU_TRACE(check_cpu_stalls());
if (user || rcu_is_cpu_rrupt_from_idle())
- rcu_sched_qs(cpu);
+ rcu_sched_qs();
else if (!in_softirq())
- rcu_bh_qs(cpu);
+ rcu_bh_qs();
if (user)
rcu_note_voluntary_context_switch(current);
}
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 0d9ee1e4f446..de234008e2c5 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -188,22 +188,24 @@ static int rcu_gp_in_progress(struct rcu_state *rsp)
* one since the start of the grace period, this just sets a flag.
* The caller must have disabled preemption.
*/
-void rcu_sched_qs(int cpu)
+void rcu_sched_qs(void)
{
- struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
-
- if (rdp->passed_quiesce == 0)
- trace_rcu_grace_period(TPS("rcu_sched"), rdp->gpnum, TPS("cpuqs"));
- rdp->passed_quiesce = 1;
+ if (!__this_cpu_read(rcu_sched_data.passed_quiesce)) {
+ trace_rcu_grace_period(TPS("rcu_sched"),
+ __this_cpu_read(rcu_sched_data.gpnum),
+ TPS("cpuqs"));
+ __this_cpu_write(rcu_sched_data.passed_quiesce, 1);
+ }
}
-void rcu_bh_qs(int cpu)
+void rcu_bh_qs(void)
{
- struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
-
- if (rdp->passed_quiesce == 0)
- trace_rcu_grace_period(TPS("rcu_bh"), rdp->gpnum, TPS("cpuqs"));
- rdp->passed_quiesce = 1;
+ if (!__this_cpu_read(rcu_bh_data.passed_quiesce)) {
+ trace_rcu_grace_period(TPS("rcu_bh"),
+ __this_cpu_read(rcu_bh_data.gpnum),
+ TPS("cpuqs"));
+ __this_cpu_write(rcu_bh_data.passed_quiesce, 1);
+ }
}
static DEFINE_PER_CPU(int, rcu_sched_qs_mask);
@@ -278,7 +280,7 @@ static void rcu_momentary_dyntick_idle(void)
void rcu_note_context_switch(int cpu)
{
trace_rcu_utilization(TPS("Start context switch"));
- rcu_sched_qs(cpu);
+ rcu_sched_qs();
rcu_preempt_note_context_switch(cpu);
if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
rcu_momentary_dyntick_idle();
@@ -2398,8 +2400,8 @@ void rcu_check_callbacks(int cpu, int user)
* at least not while the corresponding CPU is online.
*/
- rcu_sched_qs(cpu);
- rcu_bh_qs(cpu);
+ rcu_sched_qs();
+ rcu_bh_qs();
} else if (!in_softirq()) {
@@ -2410,7 +2412,7 @@ void rcu_check_callbacks(int cpu, int user)
* critical section, so note it.
*/
- rcu_bh_qs(cpu);
+ rcu_bh_qs();
}
rcu_preempt_check_callbacks(cpu);
if (rcu_pending(cpu))
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 2a6509581f40..e25aaf235ca9 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -157,14 +157,16 @@ EXPORT_SYMBOL_GPL(rcu_batches_completed);
* As with the other rcu_*_qs() functions, callers to this function
* must disable preemption.
*/
-static void rcu_preempt_qs(int cpu)
-{
- struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
-
- if (rdp->passed_quiesce == 0)
- trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs"));
- rdp->passed_quiesce = 1;
- current->rcu_read_unlock_special.b.need_qs = false;
+static void rcu_preempt_qs(void)
+{
+ if (!__this_cpu_read(rcu_preempt_data.passed_quiesce)) {
+ trace_rcu_grace_period(TPS("rcu_preempt"),
+ __this_cpu_read(rcu_preempt_data.gpnum),
+ TPS("cpuqs"));
+ __this_cpu_write(rcu_preempt_data.passed_quiesce, 1);
+ barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
+ current->rcu_read_unlock_special.b.need_qs = false;
+ }
}
/*
@@ -255,7 +257,7 @@ static void rcu_preempt_note_context_switch(int cpu)
* grace period, then the fact that the task has been enqueued
* means that we continue to block the current grace period.
*/
- rcu_preempt_qs(cpu);
+ rcu_preempt_qs();
}
/*
@@ -351,7 +353,7 @@ void rcu_read_unlock_special(struct task_struct *t)
*/
special = t->rcu_read_unlock_special;
if (special.b.need_qs) {
- rcu_preempt_qs(smp_processor_id());
+ rcu_preempt_qs();
if (!t->rcu_read_unlock_special.s) {
local_irq_restore(flags);
return;
@@ -651,11 +653,12 @@ static void rcu_preempt_check_callbacks(int cpu)
struct task_struct *t = current;
if (t->rcu_read_lock_nesting == 0) {
- rcu_preempt_qs(cpu);
+ rcu_preempt_qs();
return;
}
if (t->rcu_read_lock_nesting > 0 &&
- per_cpu(rcu_preempt_data, cpu).qs_pending)
+ per_cpu(rcu_preempt_data, cpu).qs_pending &&
+ !per_cpu(rcu_preempt_data, cpu).passed_quiesce)
t->rcu_read_unlock_special.b.need_qs = true;
}
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 5918d227730f..348ec763b104 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -278,7 +278,7 @@ restart:
pending >>= softirq_bit;
}
- rcu_bh_qs(smp_processor_id());
+ rcu_bh_qs();
local_irq_disable();
pending = local_softirq_pending();
--
1.8.1.5
--
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