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rcu: Move quiescent-state forcing into kthread
As the first step towards allowing quiescent-state forcing to be preemptible, this commit moves RCU quiescent-state forcing into the same kthread that is now used to initialize and clean up after grace periods. This is yet another step towards keeping scheduling latency down to a dull roar. Updated to change from raw_spin_lock_irqsave() to raw_spin_lock_irq() and to remove the now-unused rcu_state structure fields as suggested by Peter Zijlstra. Reported-by: Mike Galbraith <mgalbraith@suse.de> Reported-by: Dimitri Sivanich <sivanich@sgi.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney
parent
b402b73b3a
commit
4cdfc175c2
199
kernel/rcutree.c
199
kernel/rcutree.c
@ -72,7 +72,6 @@ static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
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.orphan_nxttail = &sname##_state.orphan_nxtlist, \
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.orphan_donetail = &sname##_state.orphan_donelist, \
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.barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
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.fqslock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.fqslock), \
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.name = #sname, \
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}
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@ -226,7 +225,8 @@ int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
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module_param(rcu_cpu_stall_suppress, int, 0644);
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module_param(rcu_cpu_stall_timeout, int, 0644);
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static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
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static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *));
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static void force_quiescent_state(struct rcu_state *rsp);
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static int rcu_pending(int cpu);
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/*
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@ -252,7 +252,7 @@ EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
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*/
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void rcu_bh_force_quiescent_state(void)
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{
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force_quiescent_state(&rcu_bh_state, 0);
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force_quiescent_state(&rcu_bh_state);
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}
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EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
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@ -286,7 +286,7 @@ EXPORT_SYMBOL_GPL(rcutorture_record_progress);
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*/
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void rcu_sched_force_quiescent_state(void)
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{
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force_quiescent_state(&rcu_sched_state, 0);
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force_quiescent_state(&rcu_sched_state);
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}
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EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
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@ -784,11 +784,11 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
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else if (!trigger_all_cpu_backtrace())
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dump_stack();
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/* If so configured, complain about tasks blocking the grace period. */
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/* Complain about tasks blocking the grace period. */
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rcu_print_detail_task_stall(rsp);
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force_quiescent_state(rsp, 0); /* Kick them all. */
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force_quiescent_state(rsp); /* Kick them all. */
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}
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static void print_cpu_stall(struct rcu_state *rsp)
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@ -1036,7 +1036,7 @@ static int rcu_gp_init(struct rcu_state *rsp)
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struct rcu_node *rnp = rcu_get_root(rsp);
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raw_spin_lock_irq(&rnp->lock);
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rsp->gp_flags = 0;
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rsp->gp_flags = 0; /* Clear all flags: New grace period. */
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if (rcu_gp_in_progress(rsp)) {
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/* Grace period already in progress, don't start another. */
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@ -1044,22 +1044,9 @@ static int rcu_gp_init(struct rcu_state *rsp)
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return 0;
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}
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if (rsp->fqs_active) {
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/*
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* We need a grace period, but force_quiescent_state()
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* is running. Tell it to start one on our behalf.
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*/
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rsp->fqs_need_gp = 1;
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raw_spin_unlock_irq(&rnp->lock);
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return 0;
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}
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/* Advance to a new grace period and initialize state. */
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rsp->gpnum++;
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trace_rcu_grace_period(rsp->name, rsp->gpnum, "start");
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WARN_ON_ONCE(rsp->fqs_state == RCU_GP_INIT);
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rsp->fqs_state = RCU_GP_INIT; /* Stop force_quiescent_state. */
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rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
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record_gp_stall_check_time(rsp);
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raw_spin_unlock_irq(&rnp->lock);
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@ -1096,19 +1083,40 @@ static int rcu_gp_init(struct rcu_state *rsp)
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cond_resched();
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}
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rnp = rcu_get_root(rsp);
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raw_spin_lock_irq(&rnp->lock);
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/* force_quiescent_state() now OK. */
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rsp->fqs_state = RCU_SIGNAL_INIT;
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raw_spin_unlock_irq(&rnp->lock);
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put_online_cpus();
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return 1;
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}
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/*
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* Do one round of quiescent-state forcing.
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*/
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int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
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{
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int fqs_state = fqs_state_in;
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struct rcu_node *rnp = rcu_get_root(rsp);
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rsp->n_force_qs++;
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if (fqs_state == RCU_SAVE_DYNTICK) {
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/* Collect dyntick-idle snapshots. */
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force_qs_rnp(rsp, dyntick_save_progress_counter);
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fqs_state = RCU_FORCE_QS;
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} else {
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/* Handle dyntick-idle and offline CPUs. */
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force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
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}
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/* Clear flag to prevent immediate re-entry. */
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if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
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raw_spin_lock_irq(&rnp->lock);
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rsp->gp_flags &= ~RCU_GP_FLAG_FQS;
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raw_spin_unlock_irq(&rnp->lock);
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}
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return fqs_state;
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}
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/*
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* Clean up after the old grace period.
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*/
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static int rcu_gp_cleanup(struct rcu_state *rsp)
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static void rcu_gp_cleanup(struct rcu_state *rsp)
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{
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unsigned long gp_duration;
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struct rcu_data *rdp;
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@ -1160,7 +1168,6 @@ static int rcu_gp_cleanup(struct rcu_state *rsp)
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if (cpu_needs_another_gp(rsp, rdp))
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rsp->gp_flags = 1;
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raw_spin_unlock_irq(&rnp->lock);
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return 1;
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}
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/*
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@ -1168,6 +1175,8 @@ static int rcu_gp_cleanup(struct rcu_state *rsp)
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*/
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static int __noreturn rcu_gp_kthread(void *arg)
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{
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int fqs_state;
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int ret;
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struct rcu_state *rsp = arg;
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struct rcu_node *rnp = rcu_get_root(rsp);
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@ -1175,26 +1184,43 @@ static int __noreturn rcu_gp_kthread(void *arg)
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/* Handle grace-period start. */
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for (;;) {
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wait_event_interruptible(rsp->gp_wq, rsp->gp_flags);
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if (rsp->gp_flags && rcu_gp_init(rsp))
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wait_event_interruptible(rsp->gp_wq,
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rsp->gp_flags &
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RCU_GP_FLAG_INIT);
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if ((rsp->gp_flags & RCU_GP_FLAG_INIT) &&
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rcu_gp_init(rsp))
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break;
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cond_resched();
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flush_signals(current);
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}
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/* Handle grace-period end. */
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rnp = rcu_get_root(rsp);
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/* Handle quiescent-state forcing. */
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fqs_state = RCU_SAVE_DYNTICK;
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for (;;) {
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wait_event_interruptible(rsp->gp_wq,
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!ACCESS_ONCE(rnp->qsmask) &&
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!rcu_preempt_blocked_readers_cgp(rnp));
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rsp->jiffies_force_qs = jiffies +
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RCU_JIFFIES_TILL_FORCE_QS;
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ret = wait_event_interruptible_timeout(rsp->gp_wq,
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(rsp->gp_flags & RCU_GP_FLAG_FQS) ||
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(!ACCESS_ONCE(rnp->qsmask) &&
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!rcu_preempt_blocked_readers_cgp(rnp)),
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RCU_JIFFIES_TILL_FORCE_QS);
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/* If grace period done, leave loop. */
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if (!ACCESS_ONCE(rnp->qsmask) &&
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!rcu_preempt_blocked_readers_cgp(rnp) &&
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rcu_gp_cleanup(rsp))
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!rcu_preempt_blocked_readers_cgp(rnp))
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break;
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cond_resched();
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flush_signals(current);
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/* If time for quiescent-state forcing, do it. */
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if (ret == 0 || (rsp->gp_flags & RCU_GP_FLAG_FQS)) {
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fqs_state = rcu_gp_fqs(rsp, fqs_state);
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cond_resched();
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} else {
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/* Deal with stray signal. */
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cond_resched();
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flush_signals(current);
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}
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}
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/* Handle grace-period end. */
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rcu_gp_cleanup(rsp);
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}
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}
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@ -1226,7 +1252,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
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return;
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}
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rsp->gp_flags = 1;
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rsp->gp_flags = RCU_GP_FLAG_INIT;
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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wake_up(&rsp->gp_wq);
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}
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@ -1777,72 +1803,20 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
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* Force quiescent states on reluctant CPUs, and also detect which
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* CPUs are in dyntick-idle mode.
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*/
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static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
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static void force_quiescent_state(struct rcu_state *rsp)
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{
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unsigned long flags;
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struct rcu_node *rnp = rcu_get_root(rsp);
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trace_rcu_utilization("Start fqs");
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if (!rcu_gp_in_progress(rsp)) {
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trace_rcu_utilization("End fqs");
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return; /* No grace period in progress, nothing to force. */
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}
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if (!raw_spin_trylock_irqsave(&rsp->fqslock, flags)) {
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if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS)
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return; /* Someone beat us to it. */
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if (!raw_spin_trylock_irqsave(&rnp->lock, flags)) {
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rsp->n_force_qs_lh++; /* Inexact, can lose counts. Tough! */
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trace_rcu_utilization("End fqs");
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return; /* Someone else is already on the job. */
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}
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if (relaxed && ULONG_CMP_GE(rsp->jiffies_force_qs, jiffies))
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goto unlock_fqs_ret; /* no emergency and done recently. */
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rsp->n_force_qs++;
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raw_spin_lock(&rnp->lock); /* irqs already disabled */
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rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
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if(!rcu_gp_in_progress(rsp)) {
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rsp->n_force_qs_ngp++;
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raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
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goto unlock_fqs_ret; /* no GP in progress, time updated. */
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}
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rsp->fqs_active = 1;
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switch (rsp->fqs_state) {
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case RCU_GP_IDLE:
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case RCU_GP_INIT:
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break; /* grace period idle or initializing, ignore. */
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case RCU_SAVE_DYNTICK:
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raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
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/* Record dyntick-idle state. */
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force_qs_rnp(rsp, dyntick_save_progress_counter);
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raw_spin_lock(&rnp->lock); /* irqs already disabled */
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if (rcu_gp_in_progress(rsp))
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rsp->fqs_state = RCU_FORCE_QS;
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break;
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case RCU_FORCE_QS:
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/* Check dyntick-idle state, send IPI to laggarts. */
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raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
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force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
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/* Leave state in case more forcing is required. */
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raw_spin_lock(&rnp->lock); /* irqs already disabled */
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break;
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}
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rsp->fqs_active = 0;
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if (rsp->fqs_need_gp) {
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raw_spin_unlock(&rsp->fqslock); /* irqs remain disabled */
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rsp->fqs_need_gp = 0;
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rcu_start_gp(rsp, flags); /* releases rnp->lock */
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trace_rcu_utilization("End fqs");
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return;
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}
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raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
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unlock_fqs_ret:
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raw_spin_unlock_irqrestore(&rsp->fqslock, flags);
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trace_rcu_utilization("End fqs");
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rsp->gp_flags |= RCU_GP_FLAG_FQS;
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */
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}
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/*
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@ -1858,13 +1832,6 @@ __rcu_process_callbacks(struct rcu_state *rsp)
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WARN_ON_ONCE(rdp->beenonline == 0);
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/*
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* If an RCU GP has gone long enough, go check for dyntick
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* idle CPUs and, if needed, send resched IPIs.
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*/
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if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
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force_quiescent_state(rsp, 1);
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/*
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* Advance callbacks in response to end of earlier grace
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* period that some other CPU ended.
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@ -1965,12 +1932,11 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
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rdp->blimit = LONG_MAX;
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if (rsp->n_force_qs == rdp->n_force_qs_snap &&
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*rdp->nxttail[RCU_DONE_TAIL] != head)
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force_quiescent_state(rsp, 0);
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force_quiescent_state(rsp);
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rdp->n_force_qs_snap = rsp->n_force_qs;
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rdp->qlen_last_fqs_check = rdp->qlen;
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}
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} else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
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force_quiescent_state(rsp, 1);
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}
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}
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static void
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@ -2251,17 +2217,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
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/* Is the RCU core waiting for a quiescent state from this CPU? */
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if (rcu_scheduler_fully_active &&
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rdp->qs_pending && !rdp->passed_quiesce) {
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/*
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* If force_quiescent_state() coming soon and this CPU
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* needs a quiescent state, and this is either RCU-sched
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* or RCU-bh, force a local reschedule.
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*/
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rdp->n_rp_qs_pending++;
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if (!rdp->preemptible &&
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ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs) - 1,
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jiffies))
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set_need_resched();
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} else if (rdp->qs_pending && rdp->passed_quiesce) {
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rdp->n_rp_report_qs++;
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return 1;
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@ -2291,13 +2247,6 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
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return 1;
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}
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/* Has an RCU GP gone long enough to send resched IPIs &c? */
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if (rcu_gp_in_progress(rsp) &&
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ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) {
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rdp->n_rp_need_fqs++;
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return 1;
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}
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/* nothing to do */
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rdp->n_rp_need_nothing++;
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return 0;
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@ -378,13 +378,6 @@ struct rcu_state {
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u8 fqs_state ____cacheline_internodealigned_in_smp;
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/* Force QS state. */
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u8 fqs_active; /* force_quiescent_state() */
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/* is running. */
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u8 fqs_need_gp; /* A CPU was prevented from */
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/* starting a new grace */
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/* period because */
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/* force_quiescent_state() */
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/* was running. */
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u8 boost; /* Subject to priority boost. */
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unsigned long gpnum; /* Current gp number. */
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unsigned long completed; /* # of last completed gp. */
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@ -413,8 +406,6 @@ struct rcu_state {
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struct completion barrier_completion; /* Wake at barrier end. */
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unsigned long n_barrier_done; /* ++ at start and end of */
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/* _rcu_barrier(). */
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raw_spinlock_t fqslock; /* Only one task forcing */
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/* quiescent states. */
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unsigned long jiffies_force_qs; /* Time at which to invoke */
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/* force_quiescent_state(). */
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unsigned long n_force_qs; /* Number of calls to */
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@ -433,6 +424,10 @@ struct rcu_state {
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struct list_head flavors; /* List of RCU flavors. */
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};
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/* Values for rcu_state structure's gp_flags field. */
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#define RCU_GP_FLAG_INIT 0x1 /* Need grace-period initialization. */
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#define RCU_GP_FLAG_FQS 0x2 /* Need grace-period quiescent-state forcing. */
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extern struct list_head rcu_struct_flavors;
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#define for_each_rcu_flavor(rsp) \
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list_for_each_entry((rsp), &rcu_struct_flavors, flavors)
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@ -119,7 +119,7 @@ EXPORT_SYMBOL_GPL(rcu_batches_completed);
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*/
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void rcu_force_quiescent_state(void)
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{
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force_quiescent_state(&rcu_preempt_state, 0);
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force_quiescent_state(&rcu_preempt_state);
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}
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EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
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@ -2076,16 +2076,16 @@ static void rcu_prepare_for_idle(int cpu)
|
||||
#ifdef CONFIG_TREE_PREEMPT_RCU
|
||||
if (per_cpu(rcu_preempt_data, cpu).nxtlist) {
|
||||
rcu_preempt_qs(cpu);
|
||||
force_quiescent_state(&rcu_preempt_state, 0);
|
||||
force_quiescent_state(&rcu_preempt_state);
|
||||
}
|
||||
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
|
||||
if (per_cpu(rcu_sched_data, cpu).nxtlist) {
|
||||
rcu_sched_qs(cpu);
|
||||
force_quiescent_state(&rcu_sched_state, 0);
|
||||
force_quiescent_state(&rcu_sched_state);
|
||||
}
|
||||
if (per_cpu(rcu_bh_data, cpu).nxtlist) {
|
||||
rcu_bh_qs(cpu);
|
||||
force_quiescent_state(&rcu_bh_state, 0);
|
||||
force_quiescent_state(&rcu_bh_state);
|
||||
}
|
||||
|
||||
/*
|
||||
|
||||
Loading…
Reference in New Issue
Block a user