Commit c9e8afb8 authored May 08, 2017 by Kaushal Kumar Committed by Kyle Yan Jun 12, 2017

sched: Remove synchronize rcu/sched calls from _cpu_down



There is no need for sync_sched() in _cpu_down as stop_machine()
provides that barrier implicitly. Removing it also helps improve
hot-unplug latency.

The sync_sched/rcu were earlier removed for the same reason by the
commit 9ee349ad ("sched: Fix set_cpu_active() in cpu_down()"),
but recently got added as part of commit <6acce3ef> ("sched:
Remove get_online_cpus() usage.").

CRs-Fixed: 2044149
Change-Id: I97763004454d082d3cc2d9d9dbef7da923608600
Signed-off-by: Kaushal Kumar <kaushalk@codeaurora.org>
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>
Signed-off-by: Trilok Soni <tsoni@codeaurora.org>

parent a3ba7da6

kernel/sched/core.c

+0 −14

Original line number	Diff line number	Diff line
		@@ -8052,20 +8052,6 @@ int sched_cpu_deactivate(unsigned int cpu)
		int ret;

		set_cpu_active(cpu, false);
		/*
		* We've cleared cpu_active_mask, wait for all preempt-disabled and RCU
		* users of this state to go away such that all new such users will
		* observe it.
		*
		* For CONFIG_PREEMPT we have preemptible RCU and its sync_rcu() might
		* not imply sync_sched(), so wait for both.
		*
		* Do sync before park smpboot threads to take care the rcu boost case.
		*/
		if (IS_ENABLED(CONFIG_PREEMPT))
		synchronize_rcu_mult(call_rcu, call_rcu_sched);
		else
		synchronize_rcu();

		if (!sched_smp_initialized)
		return 0;