On Wed, 20 Apr 2022 09:13:19 -0700 "Paul E. McKenney" <paulmck@xxxxxxxxxx> wrote: > > > +The tasks-rude-RCU API is also reader-marking-free and thus quite compact, > > > +consisting of call_rcu_tasks_rude(), synchronize_rcu_tasks_rude(), > > > +and rcu_barrier_tasks_rude(). > > > > Are we going to be able to get rid of the "rude" version once we have all > > tracing in a RCU visible section? > > You tell me! ;-) > > If there are no longer any users, I would be happy to get rid of it. > As of v5.18-rc1, the only user is ftrace. > > > > + > > > +Tasks Trace RCU > > > +~~~~~~~~~~~~~~~ > > > + > > > +Some forms of tracing need to sleep in readers, but cannot tolerate > > > +SRCU's read-side overhead, which includes a full memory barrier in both > > > +srcu_read_lock() and srcu_read_unlock(). This need is handled by a > > > +Tasks Trace RCU that uses scheduler locking and IPIs to synchronize with > > > +readers. Real-time systems that cannot tolerate IPIs may build their > > > +kernels with ``CONFIG_TASKS_TRACE_RCU_READ_MB=y``, which avoids the IPIs at > > > +the expense of adding full memory barriers to the read-side primitives. > > > > If NOHZ_FULL is enabled, is there a way to also be able to have this full > > mb on RT removed as well? > > Hmm, if we no longer need the rude version due to noinstr, if then we need to use something that adds full memory barriers at *every function call* then I rather keep the rude version. -- Steve
