Currently, rcu_do_batch() invokes rcu_segcblist_is_offloaded() each time
it needs to know whether the current CPU is a no-CBs CPU. Given that it
is not possible to change the no-CBs status of a CPU after boot, and given
that it is not possible to even have no-CBs CPUs in CONFIG_RCU_NOCB_CPU=n
kernels, this per-callback invocation wastes CPU. This commit therefore
created a const on-stack variable to allow this check to be done only
once per rcu_do_batch() invocation.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx>
---
kernel/rcu/tree.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e5f30b364276..16dabd6b36d7 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2087,6 +2087,8 @@ int rcutree_dead_cpu(unsigned int cpu)
static void rcu_do_batch(struct rcu_data *rdp)
{
unsigned long flags;
+ const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
+ rcu_segcblist_is_offloaded(&rdp->cblist);
struct rcu_head *rhp;
struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
long bl, count;
@@ -2128,12 +2130,11 @@ static void rcu_do_batch(struct rcu_data *rdp)
* Stop only if limit reached and CPU has something to do.
* Note: The rcl structure counts down from zero.
*/
- if (-rcl.len >= bl &&
- !rcu_segcblist_is_offloaded(&rdp->cblist) &&
+ if (-rcl.len >= bl && !offloaded &&
(need_resched() ||
(!is_idle_task(current) && !rcu_is_callbacks_kthread())))
break;
- if (rcu_segcblist_is_offloaded(&rdp->cblist)) {
+ if (offloaded) {
WARN_ON_ONCE(in_serving_softirq());
local_bh_enable();
lockdep_assert_irqs_enabled();
@@ -2175,8 +2176,7 @@ static void rcu_do_batch(struct rcu_data *rdp)
rcu_nocb_unlock_irqrestore(rdp, flags);
/* Re-invoke RCU core processing if there are callbacks remaining. */
- if (!rcu_segcblist_is_offloaded(&rdp->cblist) &&
- rcu_segcblist_ready_cbs(&rdp->cblist))
+ if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist))
invoke_rcu_core();
}
--
2.17.1
