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Commit 779de6ce authored by Paul E. McKenney's avatar Paul E. McKenney
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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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent ec90a194

kernel/cpu.c

+5 −5
Original line number Diff line number Diff line
@@ -380,13 +380,13 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) 
	 * will observe it.

	 *

	 * For CONFIG_PREEMPT we have preemptible RCU and its sync_rcu() might

	 * not imply sync_sched(), so explicitly call both.

	 * not imply sync_sched(), so wait for both.

	 *

	 * Do sync before park smpboot threads to take care the rcu boost case.

	 */

#ifdef CONFIG_PREEMPT

	synchronize_sched();

#endif

	if (IS_ENABLED(CONFIG_PREEMPT))

		synchronize_rcu_mult(call_rcu, call_rcu_sched);

	else

		synchronize_rcu();



	smpboot_park_threads(cpu);