At present, during the cpu teardown, rcu_boost_kthread_setaffinity() is called twice. Firstly by rcutree_offline_cpu(), then by rcutree_dead_cpu() as the CPUHP_RCUTREE_PREP cpuhp_step callback. >From the scheduler's perspective, a bit in cpu_online_mask means that the cpu is visible to the scheduler. Furthermore, a bit in cpu_active_mask means that the cpu is suitable as a migration destination. Now turning back to the case in rcu offlining. sched_cpu_deactivate() has disabled the dying cpu as the migration destination before rcutree_offline_cpu(). Furthermore, if the boost kthread is on the dying cpu, it will be migrated to another suitable online cpu by the scheduler. So the affinity setting by rcutree_offline_cpu() is redundant and can be eliminated. Besides, this patch does an trival code rearrangement by unfolding rcutree_affinity_setting() into rcutree_online_cpu(), considering that the latter one is the only user of the former. Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx> Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx> Cc: David Woodhouse <dwmw@xxxxxxxxxxxx> Cc: Frederic Weisbecker <frederic@xxxxxxxxxx> Cc: Neeraj Upadhyay <quic_neeraju@xxxxxxxxxxx> Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx> Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> Cc: "Jason A. Donenfeld" <Jason@xxxxxxxxx> To: rcu@xxxxxxxxxxxxxxx --- kernel/rcu/tree.c | 14 +------------- 1 file changed, 1 insertion(+), 13 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 79aea7df4345..b90f6487fd45 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3978,16 +3978,6 @@ int rcutree_prepare_cpu(unsigned int cpu) return 0; } -/* - * Update RCU priority boot kthread affinity for CPU-hotplug changes. - */ -static void rcutree_affinity_setting(unsigned int cpu, int outgoing) -{ - struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); - - rcu_boost_kthread_setaffinity(rdp->mynode, outgoing); -} - /* * Near the end of the CPU-online process. Pretty much all services * enabled, and the CPU is now very much alive. @@ -4006,7 +3996,7 @@ int rcutree_online_cpu(unsigned int cpu) if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) return 0; /* Too early in boot for scheduler work. */ sync_sched_exp_online_cleanup(cpu); - rcutree_affinity_setting(cpu, -1); + rcu_boost_kthread_setaffinity(rdp->mynode, -1); // Stop-machine done, so allow nohz_full to disable tick. tick_dep_clear(TICK_DEP_BIT_RCU); @@ -4029,8 +4019,6 @@ int rcutree_offline_cpu(unsigned int cpu) rnp->ffmask &= ~rdp->grpmask; raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - rcutree_affinity_setting(cpu, cpu); - // nohz_full CPUs need the tick for stop-machine to work quickly tick_dep_set(TICK_DEP_BIT_RCU); return 0; -- 2.31.1