Revert "rcu: Decrease memory-barrier usage based on semi-formal proof"
This reverts commit e59fb3120becfb36b22ddb8bd27d065d3cdca499.
This reversion was due to (extreme) boot-time slowdowns on SPARC seen by
Yinghai Lu and on x86 by Ingo
.
This is a non-trivial reversion due to intervening commits.
Conflicts:
Documentation/RCU/trace.txt
kernel/rcutree.c
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index ed339702..3f6559a 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1520,6 +1520,7 @@
{
int c = 0;
int snap;
+ int snap_nmi;
int thatcpu;
/* Check for being in the holdoff period. */
@@ -1530,10 +1531,10 @@
for_each_online_cpu(thatcpu) {
if (thatcpu == cpu)
continue;
- snap = atomic_add_return(0, &per_cpu(rcu_dynticks,
- thatcpu).dynticks);
+ snap = per_cpu(rcu_dynticks, thatcpu).dynticks;
+ snap_nmi = per_cpu(rcu_dynticks, thatcpu).dynticks_nmi;
smp_mb(); /* Order sampling of snap with end of grace period. */
- if ((snap & 0x1) != 0) {
+ if (((snap & 0x1) != 0) || ((snap_nmi & 0x1) != 0)) {
per_cpu(rcu_dyntick_drain, cpu) = 0;
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
return rcu_needs_cpu_quick_check(cpu);