The following commit has been merged into the core/rcu branch of tip:
Commit-ID: faa059c397dec8a452c79e9dba64419113ea64e2
Gitweb: https://git.kernel.org/tip/faa059c397dec8a452c79e9dba64419113ea64e2
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate: Mon, 03 Feb 2020 14:20:00 -08:00
Committer: Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Thu, 20 Feb 2020 15:58:23 -08:00
rcu: Optimize and protect atomic_cmpxchg() loop
This commit reworks the atomic_cmpxchg() loop in rcu_eqs_special_set()
to do only the initial read from the current CPU's rcu_data structure's
->dynticks field explicitly. On subsequent passes, this value is instead
retained from the failing atomic_cmpxchg() operation.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
kernel/rcu/tree.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4a4a975..6c62481 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -342,14 +342,17 @@ bool rcu_eqs_special_set(int cpu)
{
int old;
int new;
+ int new_old;
struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
+ new_old = atomic_read(&rdp->dynticks);
do {
- old = atomic_read(&rdp->dynticks);
+ old = new_old;
if (old & RCU_DYNTICK_CTRL_CTR)
return false;
new = old | RCU_DYNTICK_CTRL_MASK;
- } while (atomic_cmpxchg(&rdp->dynticks, old, new) != old);
+ new_old = atomic_cmpxchg(&rdp->dynticks, old, new);
+ } while (new_old != old);
return true;
}
|