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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: Paul 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: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Paul E. McKenney 2010-02-26 16:38:58 -08:00 committed by Ingo Molnar
parent 0b1c87278a
commit 71da81324c
1 changed files with 9 additions and 1 deletions
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10
kernel/rcutree_plugin.h
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@ -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) */