During callback overload (exceeding qhimark), the NOCB code attempts opportunistic advancement via rcu_advance_cbs_nowake(). Analysis shows this code path is practically unreachable and serves no useful purpose.
Testing with 300,000 callback floods showed: - 30 overload conditions triggered - 0 advancements actually occurred While a theoretical window exists where this code could execute (e.g., vCPU preemption between gp_seq update and rcu_nocb_gp_cleanup()), even if it did, the advancement would be redundant. The rcuog kthread must still run to wake the rcuoc callback thread - we would just be duplicating work that rcuog will perform when it finally gets to run. Since this path provides no meaningful benefit and extensive testing confirms it is never useful, remove it entirely. Reviewed-by: Frederic Weisbecker <[email protected]> Reviewed-by: Paul E. McKenney <[email protected]> Signed-off-by: Joel Fernandes <[email protected]> --- kernel/rcu/tree_nocb.h | 12 ------------ 1 file changed, 12 deletions(-) diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index f525e4f7985b..64a8ff350f92 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -526,8 +526,6 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone, __releases(rdp->nocb_lock) { long bypass_len; - unsigned long cur_gp_seq; - unsigned long j; long lazy_len; long len; struct task_struct *t; @@ -562,16 +560,6 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone, } return; - } else if (len > rdp->qlen_last_fqs_check + qhimark) { - /* ... or if many callbacks queued. */ - rdp->qlen_last_fqs_check = len; - j = jiffies; - if (j != rdp->nocb_gp_adv_time && - rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) && - rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) { - rcu_advance_cbs_nowake(rdp->mynode, rdp); - rdp->nocb_gp_adv_time = j; - } } rcu_nocb_unlock(rdp); -- 2.34.1
