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

[Zhuo, Qiuxu]

> From: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
> Sent: Tuesday, February 28, 2023 10:27 PM
> To: Zhuo, Qiuxu <qiuxu.zhuo@xxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx; Frederic Weisbecker <frederic@xxxxxxxxxx>;
> Lai Jiangshan <jiangshanlai@xxxxxxxxx>; linux-doc@xxxxxxxxxxxxxxx; Paul E.
> McKenney <paulmck@xxxxxxxxxx>; rcu@xxxxxxxxxxxxxxx
> 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@xxxxxxxxx> 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