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

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Message-ID: <20200924103726.GM6442@alley>
Date:   Thu, 24 Sep 2020 12:37:26 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        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
Subject: Re: [PATCH 1/2] printk: Store all three timestamps

On Thu 2020-09-24 02:06:12, John Ogness wrote:
> 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.

I would like to have a structure if we have more timestamps.

Honestly, printk-specific structure sounds like an overhead to me.
How big is the chance that struct ktime_timestamps ts would get
modified? It has been created for printk after all.

That said, I could live with printk-specific structure.
We might even need it if we need to store also local_clock().

Best Regards,
Petr