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rcu: Make kernel-mode nohz_full CPUs invoke the RCU core processing
If a nohz_full CPU is idle or executing in userspace, it makes good sense to keep it out of RCU core processing. After all, the RCU grace-period kthread can see its quiescent states and all of its callbacks are offloaded, so there is nothing for RCU core processing to do. However, if a nohz_full CPU is executing in kernel space, the RCU grace-period kthread cannot do anything for it, so such a CPU must report its own quiescent states. This commit therefore makes nohz_full CPUs skip RCU core processing only if the scheduler-clock interrupt caught them in idle or in userspace. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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1 changed files with 5 additions and 5 deletions
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@ -497,7 +497,7 @@ module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next
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module_param(rcu_kick_kthreads, bool, 0644);
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static void force_qs_rnp(int (*f)(struct rcu_data *rdp));
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static int rcu_pending(void);
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static int rcu_pending(int user);
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/*
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* Return the number of RCU GPs completed thus far for debug & stats.
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@ -2267,7 +2267,7 @@ void rcu_sched_clock_irq(int user)
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__this_cpu_write(rcu_data.rcu_urgent_qs, false);
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}
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rcu_flavor_sched_clock_irq(user);
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if (rcu_pending())
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if (rcu_pending(user))
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invoke_rcu_core();
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trace_rcu_utilization(TPS("End scheduler-tick"));
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@ -2816,7 +2816,7 @@ EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
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* CPU-local state are performed first. However, we must check for CPU
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* stalls first, else we might not get a chance.
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*/
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static int rcu_pending(void)
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static int rcu_pending(int user)
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{
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bool gp_in_progress;
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struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
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@ -2829,8 +2829,8 @@ static int rcu_pending(void)
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if (rcu_nocb_need_deferred_wakeup(rdp))
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return 1;
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/* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
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if (rcu_nohz_full_cpu())
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/* Is this a nohz_full CPU in userspace or idle? (Ignore RCU if so.) */
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if ((user || rcu_is_cpu_rrupt_from_idle()) && rcu_nohz_full_cpu())
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return 0;
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/* Is the RCU core waiting for a quiescent state from this CPU? */
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