Commit 925da92b authored by Waiman Long's avatar Waiman Long Committed by Paul E. McKenney
Browse files

rcu: Avoid unneeded function call in rcu_read_unlock() 



Since commit aa40c138 ("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: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarWaiman Long <longman@redhat.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent f0b2b2df

include/linux/rcupdate.h

+2 −1
Original line number Diff line number Diff line
@@ -71,6 +71,7 @@ static inline void __rcu_read_lock(void) 
static inline void __rcu_read_unlock(void)

{

	preempt_enable();

	if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))

		rcu_read_unlock_strict();

}

kernel/rcu/tree_plugin.h

+1 −2
Original line number Diff line number Diff line
@@ -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);