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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: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
steinar/wifi_calib_4_9_kernel
Paul E. McKenney 2015-06-10 13:34:41 -07:00
parent ec90a194ae
commit 779de6ce54
1 changed files with 5 additions and 5 deletions
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10
kernel/cpu.c
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@ -380,14 +380,14 @@ 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
synchronize_rcu();
if (IS_ENABLED(CONFIG_PREEMPT))
synchronize_rcu_mult(call_rcu, call_rcu_sched);
else
synchronize_rcu();
smpboot_park_threads(cpu);