From: Paul E. McKenney Date: Tue, 21 May 2019 20:39:15 +0000 (-0700) Subject: rcu/nocb: Use build-time no-CBs check in rcu_core() X-Git-Tag: v5.15~5556^2~1^2^2~23 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=c1ab99d66ebcebedd9d416a840c488eaf079f3e9;p=platform%2Fkernel%2Flinux-starfive.git rcu/nocb: Use build-time no-CBs check in rcu_core() Currently, rcu_core() 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 repeated runtime invocation wastes CPU. This commit therefore created a const on-stack variable to allow this check to be done only once per rcu_core() invocation. Signed-off-by: Paul E. McKenney --- diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 16dabd6b36d7..14939273d120 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2302,6 +2302,8 @@ static __latent_entropy void rcu_core(void) unsigned long flags; struct rcu_data *rdp = raw_cpu_ptr(&rcu_data); struct rcu_node *rnp = rdp->mynode; + const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) && + rcu_segcblist_is_offloaded(&rdp->cblist); if (cpu_is_offline(smp_processor_id())) return; @@ -2321,8 +2323,7 @@ static __latent_entropy void rcu_core(void) /* No grace period and unregistered callbacks? */ if (!rcu_gp_in_progress() && - rcu_segcblist_is_enabled(&rdp->cblist) && - !rcu_segcblist_is_offloaded(&rdp->cblist)) { + rcu_segcblist_is_enabled(&rdp->cblist) && !offloaded) { local_irq_save(flags); if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) rcu_accelerate_cbs_unlocked(rnp, rdp); @@ -2332,8 +2333,7 @@ static __latent_entropy void rcu_core(void) rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check()); /* If there are callbacks ready, invoke them. */ - if (!rcu_segcblist_is_offloaded(&rdp->cblist) && - rcu_segcblist_ready_cbs(&rdp->cblist) && + if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist) && likely(READ_ONCE(rcu_scheduler_fully_active))) rcu_do_batch(rdp);