On Fri, Feb 11, 2022 at 07:42:03AM -0800, Paul E. McKenney wrote: > On Fri, Feb 11, 2022 at 04:11:48PM +0100, Frederic Weisbecker wrote: > > On Fri, Feb 11, 2022 at 03:57:57PM +0100, Frederic Weisbecker wrote: > > > On Fri, Feb 04, 2022 at 03:07:59PM -0800, Paul E. McKenney wrote: > > > > From: David Woodhouse <dwmw@xxxxxxxxxxxx> > > > > > > > > As we handle parallel CPU bringup, we will need to take care to avoid > > > > spawning multiple boost threads, or race conditions when setting their > > > > affinity. Spotted by Paul McKenney. > > > > > > > > Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx> > > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > > > > > Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx> > > > > > > Speaking of, we have: > > > > > > rcu_init() > > > for_each_online_cpu(cpu) // should be boot CPU only at this stage ? > > > rcutree_prepare_cpu(cpu) > > > rcu_spawn_one_boost_kthread(cpu) > > > > > > > > > early_initcall() > > > rcu_spawn_gp_kthread() > > > rcu_spawn_boost_kthreads() > > > rcu_for_each_leaf_node(rnp) > > > rcu_rnp_online_cpus(rnp) // as above, only boot CPU at this stage. > > > rcu_spawn_one_boost_kthread(cpu) > > > > > > cpu_up() > > > rcutree_prepare_cpu(cpu) > > > rcu_spawn_one_boost_kthread(cpu) > > > > > > > > > My guess is that we could remove rcu_spawn_boost_kthreads() and simplify > > > rcu_init(). Something like this (untested yet): > > If you also add a WARN_ON() for more than one CPU being online at > rcu_init() time, I am good with this approach. The main danger that > the pre-rcu_init() portion of the boot time becomes the long straw in > the eternal quest to make systems boot faster, but it is not hard to > put it back. Hence the WARN_ON() to make it clear that adjustment > is needed. ;-) > > Thanx, Paul Make sense. On my TODO list then. Thanks!
