Commit 696a02cc authored Feb 16, 2012 by Paul E. McKenney Committed by Paul E. McKenney Feb 21, 2012

rcu: Hold off RCU_FAST_NO_HZ after timer posted

This commit handles workloads that transition quickly between idle and
non-idle, and where the CPU's callbacks cannot be invoked, but where
RCU does not have anything immediate for the CPU to do. Without this
patch, the RCU_FAST_NO_HZ code can be invoked repeatedly on each entry
to idle. The commit sets the per-CPU rcu_dyntick_holdoff variable to
hold off further attempts for a tick.

Reported-by: "Abou Gazala, Neven M" <neven.m.abou.gazala@intel.com>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

parent c3ce910b

kernel/rcutree_plugin.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -2138,7 +2138,7 @@ static void rcu_prepare_for_idle(int cpu)
		/* Can we go dyntick-idle despite still having callbacks? */
		trace_rcu_prep_idle("Dyntick with callbacks");
		per_cpu(rcu_dyntick_drain, cpu) = 0;
		per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
		per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;
		if (rcu_cpu_has_nonlazy_callbacks(cpu))
		hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu),
		rcu_idle_gp_wait, HRTIMER_MODE_REL);

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