Although sync_rcu_exp_select_node_cpus() treats the current CPU as being
in a quiescent state, it might well migrate to some other CPU before
reaching the smp_call_function_single(), which could then result in an
unnecessary simulated self-IPI. This commit therefore instead simply
refuses to invoke smp_call_function_single() on the current CPU, which
causes the later rcu_report_exp_cpu_mult() to report this CPU's quiescent
state with less overhead.
This also reduces the rcu_exp_handler() function's state space by removing
the direct call that this smp_call_function_single() uses to emulate the
requested self-IPI.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx>
[ paulmck: Use get_cpu() instead of preempt_disable() per Joel Fernandes. ]
---
kernel/rcu/tree_exp.h | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 9c990df880d1..5390618787b6 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -384,7 +384,12 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
mask_ofl_test |= mask;
continue;
}
+ if (get_cpu() == cpu) {
+ put_cpu();
+ continue;
+ }
ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
+ put_cpu();
if (!ret) {
mask_ofl_ipi &= ~mask;
continue;
--
2.17.1
