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Message-ID: <620b475d-eef8-4396-9d3a-d3dcf1d70f9a@paulmck-laptop>
Date: Fri, 26 Jan 2024 23:07:18 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc: RCU <rcu@...r.kernel.org>, Neeraj upadhyay <Neeraj.Upadhyay@....com>,
Boqun Feng <boqun.feng@...il.com>, Hillf Danton <hdanton@...a.com>,
Joel Fernandes <joel@...lfernandes.org>,
LKML <linux-kernel@...r.kernel.org>,
Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>,
Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH v4 0/4] Reduce synchronize_rcu() latency(v4)
On Thu, Jan 04, 2024 at 05:25:06PM +0100, Uladzislau Rezki (Sony) wrote:
> This is a v4 that tends to improve synchronize_rcu() call. To be more
> specific it is about reducing a waiting time(especially worst cases)
> of caller that blocks until a grace period is elapsed.
>
> In general, this series separates synchronize_rcu() callers from other
> callbacks. We keep a dedicated an independent queue, thus the processing
> of it starts as soon as grace period is over, so there is no need to wait
> until other callbacks are processed one by one. Please note, a number of
> callbacks can be 10K, 20K, 60K and so on. That is why this series maintain
> a separate track for this call that blocks a context.
And before I forget (again), a possible follow-on to this work is to
reduce cond_synchronize_rcu() and cond_synchronize_rcu_full() latency.
Right now, these wait for a full additional grace period (and maybe
more) when the required grace period has not elapsed. In contrast,
this work might enable waiting only for the needed portion of a grace
period to elapse.
Thanx, Paul
> v3 -> v4:
> - Squash patches;
> - Add more description;
> - Fix comments based on v3 feedback.
>
> v3: https://lore.kernel.org/lkml/cd45b0b5-f86b-43fb-a5f3-47d340cd4f9f@paulmck-laptop/T/
> v2: https://lore.kernel.org/all/20231030131254.488186-1-urezki@gmail.com/T/
> v1: https://lore.kernel.org/lkml/20231025140915.590390-1-urezki@gmail.com/T/
>
> Neeraj Upadhyay (1):
> rcu: Improve handling of synchronize_rcu() users
>
> Uladzislau Rezki (Sony) (3):
> rcu: Reduce synchronize_rcu() latency
> rcu: Add a trace event for synchronize_rcu_normal()
> rcu: Support direct wake-up of synchronize_rcu() users
>
> .../admin-guide/kernel-parameters.txt | 14 +
> include/trace/events/rcu.h | 27 ++
> kernel/rcu/Kconfig.debug | 12 +
> kernel/rcu/tree.c | 361 +++++++++++++++++-
> kernel/rcu/tree.h | 19 +
> kernel/rcu/tree_exp.h | 2 +-
> 6 files changed, 433 insertions(+), 2 deletions(-)
>
> --
> 2.39.2
>
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