linux-kernel - [PATCH 0/9] rcu: Support for lazy callbacks on !CONFIG_RCU_NOCB

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Message-Id: <20230531101736.12981-1-frederic@kernel.org>
Date:   Wed, 31 May 2023 12:17:27 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     "Paul E . McKenney" <paulmck@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        rcu <rcu@...r.kernel.org>, Uladzislau Rezki <urezki@...il.com>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Giovanni Gherdovich <ggherdovich@...e.cz>
Subject: [PATCH 0/9] rcu: Support for lazy callbacks on !CONFIG_RCU_NOCB_CPU

Hi,

Here is a first attempt at providing support for lazy callbacks on
non-offloaded CPUs. I have measured interesting results on my machine
when it is mostly idle (just an idle ssh connection kept alive) with
a gain of +10% idle time. This needs more serious testing though,
especially to make sure that no performance regression is introduced.

Also I have only mildly tested on NOCB (eg: no rcutorture yet), so I
might have broken something.

Finally it's also possible that the idle time improvement is due to me
introducing a bug :)

The patches 1-5 can be considered independently from the rest.

Frederic Weisbecker (9):
  rcu: Assume IRQS disabled from rcu_report_dead()
  rcu: Use rcu_segcblist_segempty() instead of open coding it
  rcu: Rename jiffies_till_flush to jiffies_lazy_flush
  rcu: Introduce lazy queue's own qhimark
  rcu: Add rcutree.lazy_enabled boot parameter
  rcu/nocb: Rename was_alldone to was_pending
  rcu: Implement lazyness on the main segcblist level
  rcu: Make segcblist flags test strict
  rcu: Support lazy callbacks with CONFIG_RCU_NOCB=n

 .../admin-guide/kernel-parameters.txt         |   5 +
 include/linux/rcu_segcblist.h                 |  13 +-
 kernel/rcu/Kconfig                            |   2 +-
 kernel/rcu/rcu.h                              |   8 +-
 kernel/rcu/rcu_segcblist.c                    |  44 ++-
 kernel/rcu/rcu_segcblist.h                    |  32 +-
 kernel/rcu/rcuscale.c                         |   6 +-
 kernel/rcu/tree.c                             | 272 +++++++++++++++--
 kernel/rcu/tree.h                             |   9 +-
 kernel/rcu/tree_nocb.h                        | 285 +++++-------------
 10 files changed, 425 insertions(+), 251 deletions(-)

-- 
2.40.1