linux-kernel - Re: [PATCH v7 02/11] rcu: Make call

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Date:   Wed, 5 Oct 2022 13:44:01 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        paulmck@...nel.org
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        rushikesh.s.kadam@...el.com, urezki@...il.com,
        neeraj.iitr10@...il.com, frederic@...nel.org, paulmck@...nel.org,
        rostedt@...dmis.org, youssefesmat@...gle.com, surenb@...gle.com
Subject: Re: [PATCH v7 02/11] rcu: Make call_rcu() lazy to save power

On Tue, Oct 04, 2022 at 02:41:48AM +0000, Joel Fernandes (Google) wrote:
> Implement timer-based RCU callback batching (also known as lazy
> callbacks). With this we save about 5-10% of power consumed due
> to RCU requests that happen when system is lightly loaded or idle.
> 
> By default, all async callbacks (queued via call_rcu) are marked
> lazy. An alternate API call_rcu_flush() is provided for the few users,
> for example synchronize_rcu(), that need the old behavior.
> 
> The batch is flushed whenever a certain amount of time has passed, or
> the batch on a particular CPU grows too big. Also memory pressure will
> flush it in a future patch.
> 
> To handle several corner cases automagically (such as rcu_barrier() and
> hotplug), we re-use bypass lists which were originally introduced to
> address lock contention, to handle lazy CBs as well. The bypass list
> length has the lazy CB length included in it. A separate lazy CB length
> counter is also introduced to keep track of the number of lazy CBs.
> 
> Suggested-by: Paul McKenney <paulmck@...nel.org>
> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> ---
>  include/linux/rcupdate.h |   7 ++
>  kernel/rcu/Kconfig       |   8 ++
>  kernel/rcu/rcu.h         |   8 ++
>  kernel/rcu/tiny.c        |   2 +-
>  kernel/rcu/tree.c        | 129 +++++++++++++++++++-----------
>  kernel/rcu/tree.h        |  12 ++-
>  kernel/rcu/tree_exp.h    |   2 +-
>  kernel/rcu/tree_nocb.h   | 164 +++++++++++++++++++++++++++++++--------
>  8 files changed, 246 insertions(+), 86 deletions(-)
> 
Tested-by: Uladzislau Rezki (Sony) <urezki@...il.com>

for whole v7 series.

--
Uladzislau Rezki