From d11c563dd20ff35da5652c3e1c989d9e10e1d6d0 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 22 Feb 2010 17:04:50 -0800 Subject: sched: Use lockdep-based checking on rcu_dereference() Update the rcu_dereference() usages to take advantage of the new lockdep-based checking. 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: <1266887105-1528-6-git-send-email-paulmck@linux.vnet.ibm.com> [ -v2: fix allmodconfig missing symbol export build failure on x86 ] Signed-off-by: Ingo Molnar --- init/main.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'init') diff --git a/init/main.c b/init/main.c index 4cb47a159f02..c75dcd6eef09 100644 --- a/init/main.c +++ b/init/main.c @@ -416,7 +416,9 @@ static noinline void __init_refok rest_init(void) kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND); numa_default_policy(); pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES); + rcu_read_lock(); kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns); + rcu_read_unlock(); unlock_kernel(); /* -- cgit v1.2.2 From 8bd93a2c5d4cab2ae17d06350daa7dbf546a4634 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 22 Feb 2010 17:04:59 -0800 Subject: rcu: Accelerate grace period if last non-dynticked CPU Currently, rcu_needs_cpu() simply checks whether the current CPU has an outstanding RCU callback, which means that the last CPU to go into dyntick-idle mode might wait a few ticks for the relevant grace periods to complete. However, if all the other CPUs are in dyntick-idle mode, and if this CPU is in a quiescent state (which it is for RCU-bh and RCU-sched any time that we are considering going into dyntick-idle mode), then the grace period is instantly complete. This patch therefore repeatedly invokes the RCU grace-period machinery in order to force any needed grace periods to complete quickly. It does so a limited number of times in order to prevent starvation by an RCU callback function that might pass itself to call_rcu(). However, if any CPU other than the current one is not in dyntick-idle mode, fall back to simply checking (with fix to bug noted by Lai Jiangshan). Also, take advantage of last grace-period forcing, the opportunity to do so noted by Steve Rostedt. And apply simplified #ifdef condition suggested by Frederic Weisbecker. 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: <1266887105-1528-15-git-send-email-paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar --- init/Kconfig | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) (limited to 'init') diff --git a/init/Kconfig b/init/Kconfig index d95ca7cd5d45..42bf914b325a 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -396,6 +396,22 @@ config RCU_FANOUT_EXACT Say N if unsure. +config RCU_FAST_NO_HZ + bool "Accelerate last non-dyntick-idle CPU's grace periods" + depends on TREE_RCU && NO_HZ && SMP + default n + help + This option causes RCU to attempt to accelerate grace periods + in order to allow the final CPU to enter dynticks-idle state + more quickly. On the other hand, this option increases the + overhead of the dynticks-idle checking, particularly on systems + with large numbers of CPUs. + + Say Y if energy efficiency is critically important, particularly + if you have relatively few CPUs. + + Say N if you are unsure. + config TREE_RCU_TRACE def_bool RCU_TRACE && ( TREE_RCU || TREE_PREEMPT_RCU ) select DEBUG_FS -- cgit v1.2.2