On Mon, Jul 17, 2017 at 09:24:51PM +0800, Li, Aubrey wrote: > On 2017/7/14 12:05, Paul E. McKenney wrote: > > > > More specifically: rcu_needs_cpu(), rcu_prepare_for_idle(), > > rcu_cleanup_after_idle(), rcu_eqs_enter(), rcu_eqs_enter_common(), > > rcu_dynticks_eqs_enter(), do_nocb_deferred_wakeup(), > > rcu_dynticks_task_enter(), rcu_eqs_exit(), rcu_eqs_exit_common(), > > rcu_dynticks_task_exit(), rcu_dynticks_eqs_exit(). > > > > The first three (rcu_needs_cpu(), rcu_prepare_for_idle(), and > > rcu_cleanup_after_idle()) should not be significant unless you have > > CONFIG_RCU_FAST_NO_HZ=y. If you do, it would be interesting to learn > > how often invoke_rcu_core() is invoked from rcu_prepare_for_idle() > > and rcu_cleanup_after_idle(), as this can raise softirq. Also > > rcu_accelerate_cbs() and rcu_try_advance_all_cbs(). > > > > Knowing which of these is causing the most trouble might help me > > reduce the overhead in the current idle path. > > I measured two cases, nothing notable found.
So skipping rcu_idle_{enter,exit}() is not in fact needed at all?