Commit ca5c8258 authored Apr 16, 2019 by Paul E. McKenney

rcu/nocb: Remove deferred wakeup checks for extended quiescent states



The idea behind the checks for extended quiescent states at the end of
__call_rcu_nocb() is to handle cases where call_rcu() is invoked directly
from within an extended quiescent state, for example, from the idle loop.
However, this will result in a timer-mediated deferred wakeup, which
will cause the needed wakeup to happen within a jiffy or thereabouts.
There should be no forward-progress concerns, and if there are, the proper
response is to exit the extended quiescent state while executing the
endless blast of call_rcu() invocations, for example, using RCU_NONIDLE().
Given the more realistic case of an isolated call_rcu() invocation, there
should be no problem.

This commit therefore removes the checks for invoking call_rcu() within
an extended quiescent state for on no-CBs CPUs.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

parent 85f69b32

kernel/rcu/tree_plugin.h

+0 −10

Original line number	Diff line number	Diff line
		@@ -1709,16 +1709,6 @@ static bool __call_rcu_nocb(struct rcu_data rdp, struct rcu_head rhp,
		-atomic_long_read(&rdp->nocb_q_count_lazy),
		-rcu_get_n_cbs_nocb_cpu(rdp));

		/*
		* If called from an extended quiescent state with interrupts
		* disabled, invoke the RCU core in order to allow the idle-entry
		* deferred-wakeup check to function.
		*/
		if (irqs_disabled_flags(flags) &&
		!rcu_is_watching() &&
		cpu_online(smp_processor_id()))
		invoke_rcu_core();

		return true;
		}

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