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authorPaul E. McKenney <paulmck@linux.ibm.com>2019-04-16 14:48:28 -0700
committerPaul E. McKenney <paulmck@linux.ibm.com>2019-08-13 14:35:49 -0700
commit85f69b32126dcf798f2c8d69a7957ba990bc2e02 (patch)
tree469f0182ecef1d15e354c8183f0651d483a3748a /kernel/rcu
parentc00045be32fe13333ba8c62748ba04747c182838 (diff)
rcu/nocb: Check for deferred nocb wakeups before nohz_full early exit
In theory, a timer is used to defer wakeups of no-CBs grace-period kthreads when the wakeup cannot be done safely directly from the call_rcu(). In practice, the one-jiffy delay is not always consistent with timely callback invocation under heavy call_rcu() loads. Therefore, there are a number of checks for a pending deferred wakeup, including from the scheduling-clock interrupt. Unfortunately, this check follows the rcu_nohz_full_cpu() early exit, which renders it useless on such CPUs. This commit therefore moves the check for the pending deferred no-CB wakeup to precede the rcu_nohz_full_cpu() early exit. Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/tree.c8
1 files changed, 4 insertions, 4 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ea479d81da7f..f1a25d17e3a0 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2739,6 +2739,10 @@ static int rcu_pending(void)
/* Check for CPU stalls, if enabled. */
check_cpu_stall(rdp);
+ /* Does this CPU need a deferred NOCB wakeup? */
+ if (rcu_nocb_need_deferred_wakeup(rdp))
+ return 1;
+
/* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
if (rcu_nohz_full_cpu())
return 0;
@@ -2763,10 +2767,6 @@ static int rcu_pending(void)
unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
return 1;
- /* Does this CPU need a deferred NOCB wakeup? */
- if (rcu_nocb_need_deferred_wakeup(rdp))
- return 1;
-
/* nothing to do */
return 0;
}