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Commit 71da8132 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Ingo Molnar
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rcu: Fix accelerated GPs for last non-dynticked CPU 



This patch disables irqs across the call to rcu_needs_cpu().  It
also enforces a hold-off period so that the idle loop doesn't
softirq itself to death when there are lots of RCU callbacks in
flight on the last non-dynticked CPU.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1267231138-27856-3-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 0b1c8727

kernel/rcutree_plugin.h

+9 −1
Original line number Diff line number Diff line
@@ -986,6 +986,7 @@ static void rcu_needs_cpu_flush(void) 


#define RCU_NEEDS_CPU_FLUSHES 5

static DEFINE_PER_CPU(int, rcu_dyntick_drain);

static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);



/*

 * Check to see if any future RCU-related work will need to be done
@@ -1013,6 +1014,7 @@ int rcu_needs_cpu(int cpu) 
	for_each_cpu_not(thatcpu, nohz_cpu_mask)

		if (thatcpu != cpu) {

			per_cpu(rcu_dyntick_drain, cpu) = 0;

			per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;

			return rcu_needs_cpu_quick_check(cpu);

		}
@@ -1022,6 +1024,7 @@ int rcu_needs_cpu(int cpu) 
		per_cpu(rcu_dyntick_drain, cpu) = RCU_NEEDS_CPU_FLUSHES;

	} else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) {

		/* We have hit the limit, so time to give up. */

		per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;

		return rcu_needs_cpu_quick_check(cpu);

	}
@@ -1038,8 +1041,10 @@ int rcu_needs_cpu(int cpu) 
	}



	/* If RCU callbacks are still pending, RCU still needs this CPU. */

	if (c)

	if (c) {

		raise_softirq(RCU_SOFTIRQ);

		per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;

	}

	return c;

}
@@ -1050,10 +1055,13 @@ int rcu_needs_cpu(int cpu) 
static void rcu_needs_cpu_flush(void)

{

	int cpu = smp_processor_id();

	unsigned long flags;



	if (per_cpu(rcu_dyntick_drain, cpu) <= 0)

		return;

	local_irq_save(flags);

	(void)rcu_needs_cpu(cpu);

	local_irq_restore(flags);

}



#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */