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rcu: Avoid unneeded function call in rcu_read_unlock()

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Since commit aa40c138cc ("rcu: Report QS for outermost PREEMPT=n
rcu_read_unlock() for strict GPs") the function rcu_read_unlock_strict()
is invoked by the inlined rcu_read_unlock() function.  However,
rcu_read_unlock_strict() is an empty function in production kernels,
which are built with CONFIG_RCU_STRICT_GRACE_PERIOD=n.

There is a mention of rcu_read_unlock_strict() in the BPF verifier,
but this is in a deny-list, meaning that BPF does not care whether
rcu_read_unlock_strict() is ever called.

This commit therefore provides a slight performance improvement
by hoisting the check of CONFIG_RCU_STRICT_GRACE_PERIOD from
rcu_read_unlock_strict() into rcu_read_unlock(), thus avoiding the
pointless call to an empty function.

Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Waiman Long 2021-08-26 22:21:22 -04:00 committed by Paul E. McKenney
parent f0b2b2df54
commit 925da92ba5
2 changed files with 3 additions and 3 deletions
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3
include/linux/rcupdate.h
View File

@ -71,7 +71,8 @@ static inline void __rcu_read_lock(void)
static inline void __rcu_read_unlock(void)
{
preempt_enable();
rcu_read_unlock_strict();
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
rcu_read_unlock_strict();
}
static inline int rcu_preempt_depth(void)

3
kernel/rcu/tree_plugin.h
View File

@ -814,8 +814,7 @@ void rcu_read_unlock_strict(void)
{
struct rcu_data *rdp;
if (!IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ||
irqs_disabled() || preempt_count() || !rcu_state.gp_kthread)
if (irqs_disabled() || preempt_count() || !rcu_state.gp_kthread)
return;
rdp = this_cpu_ptr(&rcu_data);
rcu_report_qs_rdp(rdp);