linux-kernel - Re: [PATCH 1/2] printk: Store all three timestamps

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Message-ID: <878sd0m4c3.fsf@jogness.linutronix.de>
Date:   Thu, 24 Sep 2020 02:06:12 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Prarit Bhargava <prarit@...hat.com>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        Orson Zhai <orsonzhai@...il.com>,
        Changki Kim <changki.kim@...sung.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH 1/2] printk: Store all three timestamps

On 2020-09-23, Petr Mladek <pmladek@...e.com> wrote:
> diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringbuffer.h
> index 0adaa685d1ca..09082c8472d3 100644
> --- a/kernel/printk/printk_ringbuffer.h
> +++ b/kernel/printk/printk_ringbuffer.h
> @@ -14,7 +15,7 @@
>   */
>  struct printk_info {
>  	u64	seq;		/* sequence number */
> -	u64	ts_nsec;	/* timestamp in nanoseconds */
> +	struct ktime_timestamps ts; /* timestamps */

Until now struct printk_info has contained generic types. If we add
struct ktime_timestamps, we may start storing more than we need. For
example, if more (possibly internal) fields are added to struct
ktime_timestamps that printk doesn't care about. We may prefer to
generically and explicitly store the information we care about:

    u64 ts_mono;
    u64 ts_boot;
    u64 ts_real;

Or create our own struct printk_ts to copy the fields of interest to.

John Ogness