From b9ad4d6ed18e23b0ff6a824b925a1278625d5345 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 27 Mar 2019 09:09:47 -0700 Subject: [PATCH] rcu: Avoid self-IPI in sync_rcu_exp_select_node_cpus() 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: 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 @@ retry_ipi: 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;