linux-kernel - RE: [PATCH RFC v2] rcu: Add a minimum time for marking boot as completed

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Date:   Wed, 1 Mar 2023 01:34:11 +0000
From:   "Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>
To:     Joel Fernandes <joel@...lfernandes.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Frederic Weisbecker" <frederic@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        "rcu@...r.kernel.org" <rcu@...r.kernel.org>
Subject: RE: [PATCH RFC v2] rcu: Add a minimum time for marking boot as
 completed

> From: Joel Fernandes <joel@...lfernandes.org>
> Sent: Tuesday, February 28, 2023 10:27 PM
> To: Zhuo, Qiuxu <qiuxu.zhuo@...el.com>
> Cc: linux-kernel@...r.kernel.org; Frederic Weisbecker <frederic@...nel.org>;
> Lai Jiangshan <jiangshanlai@...il.com>; linux-doc@...r.kernel.org; Paul E.
> McKenney <paulmck@...nel.org>; rcu@...r.kernel.org
> Subject: Re: [PATCH RFC v2] rcu: Add a minimum time for marking boot as
> completed
> 
> On Tue, Feb 28, 2023 at 1:40 AM Zhuo, Qiuxu <qiuxu.zhuo@...el.com> wrote:
> >
> [...]
> > My testing showed the positive result that the OS boot time was
> > reduced by ~4.6% on my side after applying Joel’s patch.
> 
> Wow, this is great! I am guessing you have CONFIG_RCU_LAZY disabled,
> when you tested. If so, that is great news that expediting RCU for a bit longer
> improves boot time! Please confirm that your config had LAZY disabled.
> 

I confirm that CONFIG_RCU_LAZY kernel configuration was disabled in my testing.
All the kernel configurations for RCU used in my testing are as below:

     #
     # RCU Subsystem
     #
     CONFIG_TREE_RCU=y
     CONFIG_PREEMPT_RCU=y
     CONFIG_RCU_EXPERT=y
     CONFIG_SRCU=y
     CONFIG_TREE_SRCU=y
     CONFIG_TASKS_RCU_GENERIC=y
     # CONFIG_FORCE_TASKS_RCU is not set
     CONFIG_TASKS_RCU=y
     # CONFIG_FORCE_TASKS_RUDE_RCU is not set
     # CONFIG_FORCE_TASKS_TRACE_RCU is not set
     CONFIG_TASKS_TRACE_RCU=y
     CONFIG_RCU_STALL_COMMON=y
     CONFIG_RCU_NEED_SEGCBLIST=y
     CONFIG_RCU_FANOUT=32
     CONFIG_RCU_FANOUT_LEAF=16
     # CONFIG_RCU_BOOST is not set
     CONFIG_RCU_BOOT_END_DELAY=20000
     CONFIG_RCU_NOCB_CPU=y
     # CONFIG_RCU_NOCB_CPU_DEFAULT_ALL is not set
     # CONFIG_TASKS_TRACE_RCU_READ_MB is not set
     # CONFIG_RCU_LAZY is not set
     # end of RCU Subsystem

-Qiuxu