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

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Date:   Sun, 26 Feb 2023 18:07:26 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     linux-kernel@...r.kernel.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 Sun, Feb 26, 2023 at 2:45 PM Frederic Weisbecker <frederic@...nel.org> wrote:
>
> On Sat, Feb 25, 2023 at 03:34:21AM +0000, Joel Fernandes (Google) wrote:
> > On many systems, a great deal of boot happens after the kernel thinks the boot
> > has completed. It is difficult to determine if the system has really booted
> > from the kernel side.
>
> Is this only about kernel booting? What makes it hard to determine if the
> system has really booted?

Yes, I should probably clarify in the change log. It is more than the
kernel booting, it is all OS userspace code that runs as well during
which the CPU load is high (init spawning new programs such as shells,
daemons setup etc). The kernel does not know when that will complete
per-se. A timer based approach is not ideal, but it does not hurt
either IMHO. In other words, it is a "something better than nothing"
patch which reduces risk of slowness.

Thanks,

 - Joel