From fced9c8cfe6bc8a26dbbf785927aa673c83a7a35 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 26 Jul 2018 13:44:00 -0700 Subject: [PATCH] rcu: Avoid resched_cpu() when rescheduling the current CPU The resched_cpu() interface is quite handy, but it does acquire the specified CPU's runqueue lock, which does not come for free. This commit therefore substitutes the following when directing resched_cpu() at the current CPU: set_tsk_need_resched(current); set_preempt_need_resched(); Signed-off-by: Paul E. McKenney Cc: Peter Zijlstra --- kernel/rcu/tree.c | 11 +++++++---- kernel/rcu/tree_exp.h | 17 ++++++++++------- kernel/rcu/tree_plugin.h | 6 ++++-- 3 files changed, 21 insertions(+), 13 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 96731f62594a..92346ab8077d 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1354,7 +1354,8 @@ static void print_cpu_stall(void) * progress and it could be we're stuck in kernel space without context * switches for an entirely unreasonable amount of time. */ - resched_cpu(smp_processor_id()); + set_tsk_need_resched(current); + set_preempt_need_resched(); } static void check_cpu_stall(struct rcu_data *rdp) @@ -2675,10 +2676,12 @@ static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused WARN_ON_ONCE(!rdp->beenonline); /* Report any deferred quiescent states if preemption enabled. */ - if (!(preempt_count() & PREEMPT_MASK)) + if (!(preempt_count() & PREEMPT_MASK)) { rcu_preempt_deferred_qs(current); - else if (rcu_preempt_need_deferred_qs(current)) - resched_cpu(rdp->cpu); /* Provoke future context switch. */ + } else if (rcu_preempt_need_deferred_qs(current)) { + set_tsk_need_resched(current); + set_preempt_need_resched(); + } /* Update RCU state based on any recent quiescent states. */ rcu_check_quiescent_state(rdp); diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 78553a8fa3c6..030df96e0d3c 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -672,7 +672,8 @@ static void sync_rcu_exp_handler(void *unused) rcu_report_exp_rdp(rdp); } else { rdp->deferred_qs = true; - resched_cpu(rdp->cpu); + set_tsk_need_resched(t); + set_preempt_need_resched(); } return; } @@ -710,15 +711,16 @@ static void sync_rcu_exp_handler(void *unused) * because we are in an interrupt handler, which will cause that * function to take an early exit without doing anything. * - * Otherwise, use resched_cpu() to force a context switch after - * the CPU enables everything. + * Otherwise, force a context switch after the CPU enables everything. */ rdp->deferred_qs = true; if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) || - WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs())) + WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs())) { rcu_preempt_deferred_qs(t); - else - resched_cpu(rdp->cpu); + } else { + set_tsk_need_resched(t); + set_preempt_need_resched(); + } } /* PREEMPT=y, so no PREEMPT=n expedited grace period to clean up after. */ @@ -779,7 +781,8 @@ static void sync_sched_exp_handler(void *unused) __this_cpu_write(rcu_data.cpu_no_qs.b.exp, true); /* Store .exp before .rcu_urgent_qs. */ smp_store_release(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs), true); - resched_cpu(smp_processor_id()); + set_tsk_need_resched(current); + set_preempt_need_resched(); } /* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */ diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 1e80a0da7924..978ce3539809 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -791,8 +791,10 @@ static void rcu_flavor_check_callbacks(int user) if (t->rcu_read_lock_nesting > 0 || (preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) { /* No QS, force context switch if deferred. */ - if (rcu_preempt_need_deferred_qs(t)) - resched_cpu(smp_processor_id()); + if (rcu_preempt_need_deferred_qs(t)) { + set_tsk_need_resched(t); + set_preempt_need_resched(); + } } else if (rcu_preempt_need_deferred_qs(t)) { rcu_preempt_deferred_qs(t); /* Report deferred QS. */ return; -- 2.20.1