Since dynticks_idle is only ever modified by the local cpu we do
not need to use an atomic there. The weak "atomicity" of this_cpu
ops is sufficient since there is no other cpu modifying the variable.
[This is a cautious patch that leaves the barriers in place]
Signed-off-by: Christoph Lameter <c...@linux.com>
Index: linux/kernel/rcu/tree.c
===================================================================
--- linux.orig/kernel/rcu/tree.c
+++ linux/kernel/rcu/tree.c
@@ -213,7 +213,7 @@ static DEFINE_PER_CPU(struct rcu_dyntick
.dynticks = ATOMIC_INIT(1),
#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
.dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE,
- .dynticks_idle = ATOMIC_INIT(1),
+ .dynticks_idle = 1,
#endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
};
Index: linux/kernel/rcu/tree.h
===================================================================
--- linux.orig/kernel/rcu/tree.h
+++ linux/kernel/rcu/tree.h
@@ -91,7 +91,7 @@ struct rcu_dynticks {
#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
long long dynticks_idle_nesting;
/* irq/process nesting level from idle. */
- atomic_t dynticks_idle; /* Even value for idle, else odd. */
+ long dynticks_idle; /* Even value for idle, else odd. */
/* "Idle" excludes userspace execution. */
unsigned long dynticks_idle_jiffies;
/* End of last non-NMI non-idle period. */
Index: linux/kernel/rcu/tree_plugin.h
===================================================================
--- linux.orig/kernel/rcu/tree_plugin.h
+++ linux/kernel/rcu/tree_plugin.h
@@ -2644,9 +2644,9 @@ static void rcu_sysidle_enter(int irq)
j = jiffies;
ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j;
smp_mb__before_atomic();
- atomic_inc(&rdtp->dynticks_idle);
+ this_cpu_inc(rcu_dynticks.dynticks_idle);
smp_mb__after_atomic();
- WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
+ WARN_ON_ONCE(__this_cpu_read(rcu_dynticks.dynticks_idle) & 0x1);
}
/*
@@ -2712,9 +2712,9 @@ static void rcu_sysidle_exit(int irq)
/* Record end of idle period. */
smp_mb__before_atomic();
- atomic_inc(&rdtp->dynticks_idle);
+ this_cpu_inc(rcu_dynticks.dynticks_idle);
smp_mb__after_atomic();
- WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
+ WARN_ON_ONCE(!(__this_cpu_read(rcu_dynticks.dynticks_idle) & 0x1));
/*
* If we are the timekeeping CPU, we are permitted to be non-idle
@@ -2755,7 +2755,7 @@ static void rcu_sysidle_check_cpu(struct
WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
/* Pick up current idle and NMI-nesting counter and check. */
- cur = atomic_read(&rdtp->dynticks_idle);
+ cur = rdtp->dynticks_idle;
if (cur & 0x1) {
*isidle = false; /* We are not idle! */
return;
--
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