Commit-ID: 9a0c6fef423528ba5b62aa31b29aabf689eb8f70
Gitweb: http://git.kernel.org/tip/9a0c6fef423528ba5b62aa31b29aabf689eb8f70
Author: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
AuthorDate: Thu, 28 Jun 2012 12:33:51 -0700
Committer: Frederic Weisbecker <fweisbec@xxxxxxxxx>
CommitDate: Wed, 26 Sep 2012 15:44:02 +0200
rcu: Make RCU_FAST_NO_HZ handle adaptive ticks
The current implementation of RCU_FAST_NO_HZ tries reasonably hard to rid
the current CPU of RCU callbacks. This is appropriate when the CPU is
entering idle, where it doesn't have much useful to do anyway, but is most
definitely not what you want when transitioning to user-mode execution.
This commit therefore detects the adaptive-tick case, and refrains from
burning CPU time getting rid of RCU callbacks in that case.
Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
---
kernel/rcutree_plugin.h | 20 ++++++++++++++++++++
1 files changed, 20 insertions(+), 0 deletions(-)
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 9c71c1b..f921154 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1757,6 +1757,26 @@ static void rcu_prepare_for_idle(int cpu)
if (!tne)
return;
+ /* Adaptive-tick mode, where usermode execution is idle to RCU. */
+ if (!is_idle_task(current)) {
+ rdtp->dyntick_holdoff = jiffies - 1;
+ if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
+ trace_rcu_prep_idle("User dyntick with callbacks");
+ rdtp->idle_gp_timer_expires =
+ round_up(jiffies + RCU_IDLE_GP_DELAY,
+ RCU_IDLE_GP_DELAY);
+ } else if (rcu_cpu_has_callbacks(cpu)) {
+ rdtp->idle_gp_timer_expires =
+ round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY);
+ trace_rcu_prep_idle("User dyntick with lazy callbacks");
+ } else {
+ return;
+ }
+ tp = &rdtp->idle_gp_timer;
+ mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
+ return;
+ }
+
/*
* If this is an idle re-entry, for example, due to use of
* RCU_NONIDLE() or the new idle-loop tracing API within the idle
--
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