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authorThomas Gleixner <tglx@linutronix.de>2013-11-13 15:01:57 -0500
committerThomas Gleixner <tglx@linutronix.de>2013-11-19 08:59:50 -0500
commitd689fe222a858c767cb8594faf280048e532b53f (patch)
tree2ddb3ee24ce9fd2566a6fb9204ea9861a74a7404 /kernel/rcu/tree_plugin.h
parent801a76050bcf8d4e500eb8d048ff6265f37a61c8 (diff)
NOHZ: Check for nohz active instead of nohz enabled
RCU and the fine grained idle time accounting functions check tick_nohz_enabled. But that variable is merily telling that NOHZ has been enabled in the config and not been disabled on the command line. But it does not tell anything about nohz being active. That's what all this should check for. Matthew reported, that the idle accounting on his old P1 machine showed bogus values, when he enabled NOHZ in the config and did not disable it on the kernel command line. The reason is that his machine uses (refined) jiffies as a clocksource which explains why the "fine" grained accounting went into lala land, because it depends on when the system goes and leaves idle relative to the jiffies increment. Provide a tick_nohz_active indicator and let RCU and the accounting code use this instead of tick_nohz_enable. Reported-and-tested-by: Matthew Whitehead <tedheadster@gmail.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: john.stultz@linaro.org Cc: mwhitehe@redhat.com Link: http://lkml.kernel.org/r/alpine.DEB.2.02.1311132052240.30673@ionos.tec.linutronix.de
Diffstat (limited to 'kernel/rcu/tree_plugin.h')
-rw-r--r--kernel/rcu/tree_plugin.h4
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 6abb03dff5c0..08a765232432 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1632,7 +1632,7 @@ module_param(rcu_idle_gp_delay, int, 0644);
1632static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY; 1632static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1633module_param(rcu_idle_lazy_gp_delay, int, 0644); 1633module_param(rcu_idle_lazy_gp_delay, int, 0644);
1634 1634
1635extern int tick_nohz_enabled; 1635extern int tick_nohz_active;
1636 1636
1637/* 1637/*
1638 * Try to advance callbacks for all flavors of RCU on the current CPU, but 1638 * Try to advance callbacks for all flavors of RCU on the current CPU, but
@@ -1729,7 +1729,7 @@ static void rcu_prepare_for_idle(int cpu)
1729 int tne; 1729 int tne;
1730 1730
1731 /* Handle nohz enablement switches conservatively. */ 1731 /* Handle nohz enablement switches conservatively. */
1732 tne = ACCESS_ONCE(tick_nohz_enabled); 1732 tne = ACCESS_ONCE(tick_nohz_active);
1733 if (tne != rdtp->tick_nohz_enabled_snap) { 1733 if (tne != rdtp->tick_nohz_enabled_snap) {
1734 if (rcu_cpu_has_callbacks(cpu, NULL)) 1734 if (rcu_cpu_has_callbacks(cpu, NULL))
1735 invoke_rcu_core(); /* force nohz to see update. */ 1735 invoke_rcu_core(); /* force nohz to see update. */