cpu: Wait for RCU grace periods concurrently
In kernels built with CONFIG_PREEMPT, _cpu_down() waits for RCU and RCU-sched grace periods back-to-back, incurring quite a bit more latency than required. This commit therefore uses the new synchronize_rcu_mult() to allow waiting for both grace periods concurrently. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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ec90a194ae
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779de6ce54
10
kernel/cpu.c
10
kernel/cpu.c
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@ -380,14 +380,14 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
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* will observe it.
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*
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* For CONFIG_PREEMPT we have preemptible RCU and its sync_rcu() might
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* not imply sync_sched(), so explicitly call both.
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* not imply sync_sched(), so wait for both.
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*
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* Do sync before park smpboot threads to take care the rcu boost case.
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*/
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#ifdef CONFIG_PREEMPT
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synchronize_sched();
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#endif
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synchronize_rcu();
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if (IS_ENABLED(CONFIG_PREEMPT))
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synchronize_rcu_mult(call_rcu, call_rcu_sched);
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else
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synchronize_rcu();
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smpboot_park_threads(cpu);
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