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| author | Paul E. McKenney <paulmck@linux.ibm.com> | 2019-08-12 19:28:08 +0200 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.ibm.com> | 2019-08-13 23:35:49 +0200 |
| commit | 0bd55c693617cd2488378d011b66b92e1dd66ecf (patch) | |
| tree | 82c4f4c0b338421be2ad2835e9541fb97281936d /kernel/rcu | |
| parent | rcu/nocb: Suppress uninitialized false-positive in nocb_gp_wait() (diff) | |
| download | linux-0bd55c693617cd2488378d011b66b92e1dd66ecf.tar.xz linux-0bd55c693617cd2488378d011b66b92e1dd66ecf.zip | |
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.h | 16 |
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; } |