linux-kernel - Re: [RFC PATCH v4 9/9] printk: use a new ringbuffer implementation

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Message-ID: <CAHk-=wiDzz+KU-ArqpnzjYkvDtKWjUqMfiiJXpXhgYU+Wd0r-w@mail.gmail.com>
Date:   Fri, 9 Aug 2019 09:00:04 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Brendan Higgins <brendanhiggins@...gle.com>
Subject: Re: [RFC PATCH v4 9/9] printk: use a new ringbuffer implementation

On Fri, Aug 9, 2019 at 4:15 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> >
> > But I don't know what a power-off-in-laptop scenario really looks like..
>
> That's random behaviour. It's hardware & BIOS & value add. What do you
> expect?
>
> I tried on a few machines. My laptop does not retain any useful information
> and on some server box (which takes ages to boot) the memory is squeaky
> clean, i.e. the BIOS wiped it already. Some others worked with a two second
> delay between turning the remote power switch on and off.

You were there at the Intel meeting, weren't you?

This is all about the fact that "we're not getting sane and reliable
debug facilities for remote debugging". We haven't gotten them over
two decades, we're not seeing it in the future either.

So what if we _can_ get an ACPI update and in the next decade your
laptop _will_ have a memory area that doesn't get scribbled over?

Does it work today? Yes it does, but only for very special cases
(basically warm reboot with "fast boot" enabled).

But they are special cases that may be things that can be extended
upon without any actual hardware changes.

                  Linus