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>
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 @@
#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 @@
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 @@
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 @@
}
/* 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 @@
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) */
