This series removes an unnecessary wake path (WakeOvfIsDeferred) from the NOCB code and adds debugging warnings to detect any potential lost wakeups.
The WakeOvfIsDeferred code path in __call_rcu_nocb_wake() attempts to wake rcuog when the callback count exceeds qhimark and callbacks aren't done with their GP. However, testing proves this wake is always redundant or useless - in the flooding case, rcuog is always waiting for a GP to finish, so waking it up is pointless. All NOCB rcutorture scenarios pass (TREE01, TREE05, TREE08). Changes since v1: - Split into separate patches as suggested by Frederic - Removed the pairing smp_mb__after_spin_lock() in do_nocb_deferred_wakeup_timer() as noted by Frederic. Link to v1 (RFC): https://lore.kernel.org/all/[email protected]/ Joel Fernandes (3): rcu/nocb: Remove unnecessary WakeOvfIsDeferred wake path rcu/nocb: Add warning if no rcuog wake up attempt happened during overload rcu/nocb: Add warning to detect if overload advancement is ever useful kernel/rcu/tree.c | 2 ++ kernel/rcu/tree.h | 2 +- kernel/rcu/tree_nocb.h | 53 +++++++++++++++++++++--------------------- 3 files changed, 29 insertions(+), 28 deletions(-) -- 2.34.1
