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Next: [PATCH] thinkpad-acpi: fix return value of volume callbacks
From: Paul E. McKenney on 26 Feb 2010 19:40
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(a)linux.vnet.ibm.com>
---
kernel/rcutree_plugin.h | 10 +++++++++-
1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index ed241fc..464ad2c 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -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) */
--
1.6.6

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Prev: [PATCH tip/core/rcu 2/3] rcu: Make non-RCU_PROVE_LOCKING rcu_read_lock_sched_held() understand boot
Next: [PATCH] thinkpad-acpi: fix return value of volume callbacks