linux-kernel - Re: [PATCH 00/10] rcu: Allow a CPU to leave and reenter NOCB state

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Date:   Wed, 13 May 2020 11:15:37 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Josh Triplett <josh@...htriplett.org>
Subject: Re: [PATCH 00/10] rcu: Allow a CPU to leave and reenter NOCB state

On Wed, May 13, 2020 at 06:47:04PM +0200, Frederic Weisbecker wrote:
> This is a necessary step toward making nohz_full controllable through
> cpuset. Next step should be to allow a CPU to be nocb even if it wasn't
> part of the nocb set on boot.
> 
> The core design of this set is mostly based on suggestions from Paul
> of course.
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> 	rcu/nohz
> 
> HEAD: 31cb4ee9da4e9cc6314498ff22d83f0d872b1a88

Very cool!!!  A few comments on individual commits on a quick first
scan, and more later.

							Thanx, Paul

> Thanks,
> 	Frederic
> ---
> 
> Frederic Weisbecker (10):
>       rcu: Directly lock rdp->nocb_lock on nocb code entrypoints
>       rcu: Use direct rdp->nocb_lock operations on local calls
>       rcu: Make locking explicit in do_nocb_deferred_wakeup_common()
>       rcu: Implement rcu_segcblist_is_offloaded() config dependent
>       rcu: Remove useless conditional nocb unlock
>       rcu: Make nocb_cb kthread parkable
>       rcu: Temporarily assume that nohz full CPUs might not be NOCB
>       rcu: Allow to deactivate nocb on a CPU
>       rcu: Allow to re-offload a CPU that used to be nocb
>       rcu: Nocb (de)activate through sysfs
> 
> 
>  include/linux/rcu_segcblist.h |   2 +
>  include/linux/rcupdate.h      |   4 ++
>  kernel/cpu.c                  |  23 +++++++
>  kernel/rcu/rcu_segcblist.c    |   6 +-
>  kernel/rcu/rcu_segcblist.h    |   8 ++-
>  kernel/rcu/tree.c             |  24 +++----
>  kernel/rcu/tree.h             |   2 +-
>  kernel/rcu/tree_plugin.h      | 149 ++++++++++++++++++++++++++++++++++--------
>  8 files changed, 172 insertions(+), 46 deletions(-)