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rcu: Abstract the dynticks momentary-idle operation
This commit is the first step towards full abstraction of all accesses to the ->dynticks counter, implementing the previously open-coded atomic add of two in a new rcu_dynticks_momentary_idle() function. This abstraction will ease changes to the ->dynticks counter operation. Note that this commit gets rid of the smp_mb__before_atomic() and the smp_mb__after_atomic() calls that were previously present. The reason that this is OK from a memory-ordering perspective is that the atomic operation is now atomic_add_return(), which, as a value-returning atomic, guarantees full ordering. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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parent
52d7e48b86
commit
6563de9d6f
1 changed files with 14 additions and 5 deletions
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@ -281,6 +281,19 @@ static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
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#endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
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};
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/*
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* Do a double-increment of the ->dynticks counter to emulate a
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* momentary idle-CPU quiescent state.
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*/
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static void rcu_dynticks_momentary_idle(void)
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{
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struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
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int special = atomic_add_return(2, &rdtp->dynticks);
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/* It is illegal to call this from idle state. */
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WARN_ON_ONCE(!(special & 0x1));
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}
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DEFINE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr);
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EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr);
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@ -300,7 +313,6 @@ EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr);
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static void rcu_momentary_dyntick_idle(void)
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{
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struct rcu_data *rdp;
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struct rcu_dynticks *rdtp;
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int resched_mask;
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struct rcu_state *rsp;
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@ -327,10 +339,7 @@ static void rcu_momentary_dyntick_idle(void)
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* quiescent state, with no need for this CPU to do anything
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* further.
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*/
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rdtp = this_cpu_ptr(&rcu_dynticks);
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smp_mb__before_atomic(); /* Earlier stuff before QS. */
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atomic_add(2, &rdtp->dynticks); /* QS. */
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smp_mb__after_atomic(); /* Later stuff after QS. */
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rcu_dynticks_momentary_idle();
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break;
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}
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}
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