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authorPaul E. McKenney <paulmck@linux.ibm.com>2019-08-12 10:28:08 -0700
committerPaul E. McKenney <paulmck@linux.ibm.com>2019-08-13 14:35:49 -0700
commit0bd55c693617cd2488378d011b66b92e1dd66ecf (patch)
tree82c4f4c0b338421be2ad2835e9541fb97281936d /kernel/rcu
parent969974e5c51e717fc9070b00eb2f61ae589ed13d (diff)
rcu/nohz: Turn off tick for offloaded CPUs
Historically, no-CBs CPUs allowed the scheduler-clock tick to be unconditionally disabled on any transition to idle or nohz_full userspace execution (see the rcu_needs_cpu() implementations). Unfortunately, the checks used by rcu_needs_cpu() are defeated now that no-CBs CPUs use ->cblist, which might make users of battery-powered devices rather unhappy. This commit therefore adds explicit rcu_segcblist_is_offloaded() checks to return to the historical energy-efficient semantics. Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/tree_plugin.h16
1 files changed, 9 insertions, 7 deletions
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index c1dfbac8cd39..ae927710d670 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1226,10 +1226,10 @@ static void rcu_prepare_kthreads(int cpu)
#if !defined(CONFIG_RCU_FAST_NO_HZ)
/*
- * Check to see if any future RCU-related work will need to be done
- * by the current CPU, even if none need be done immediately, returning
- * 1 if so. This function is part of the RCU implementation; it is -not-
- * an exported member of the RCU API.
+ * Check to see if any future non-offloaded RCU-related work will need
+ * to be done by the current CPU, even if none need be done immediately,
+ * returning 1 if so. This function is part of the RCU implementation;
+ * it is -not- an exported member of the RCU API.
*
* Because we not have RCU_FAST_NO_HZ, just check whether or not this
* CPU has RCU callbacks queued.
@@ -1237,7 +1237,8 @@ static void rcu_prepare_kthreads(int cpu)
int rcu_needs_cpu(u64 basemono, u64 *nextevt)
{
*nextevt = KTIME_MAX;
- return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist);
+ return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
+ !rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist);
}
/*
@@ -1338,8 +1339,9 @@ int rcu_needs_cpu(u64 basemono, u64 *nextevt)
lockdep_assert_irqs_disabled();
- /* If no callbacks, RCU doesn't need the CPU. */
- if (rcu_segcblist_empty(&rdp->cblist)) {
+ /* If no non-offloaded callbacks, RCU doesn't need the CPU. */
+ if (rcu_segcblist_empty(&rdp->cblist) ||
+ rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist)) {
*nextevt = KTIME_MAX;
return 0;
}