linux-kernel - Re: [PATCH printk v5 6/8] printk: nbcon: Add sequence handling

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Date:   Mon, 18 Sep 2023 16:35:44 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH printk v5 6/8] printk: nbcon: Add sequence handling

On Sat 2023-09-16 21:26:05, John Ogness wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> Add an atomic_long_t field @nbcon_seq to the console struct to
> store the sequence number for nbcon consoles. For nbcon consoles
> this will be used instead of the non-atomic @seq field. The new
> field allows for safe atomic sequence number updates without
> requiring any locking.
> 
> On 64bit systems the new field stores the full sequence number.
> On 32bit systems the new field stores the lower 32 bits of the
> sequence number, which are expanded to 64bit as needed by
> folding the values based on the sequence numbers available in
> the ringbuffer.
> 
> For 32bit systems, having a 32bit representation in the console
> is sufficient. If a console ever gets more than 2^31 records
> behind the ringbuffer then this is the least of the problems.
> 
> Co-developed-by: John Ogness <john.ogness@...utronix.de>
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
> Signed-off-by: Thomas Gleixner (Intel) <tglx@...utronix.de>

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr