From 71da81324c83ef65bb196c7f874ac1c6996d8287 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 26 Feb 2010 16:38:58 -0800 Subject: 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 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 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) */ -- cgit v0.10.2