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 <[email protected]> --- 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
