linux-kernel - Re: [GIT pull] printk updates for 4.15

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Date:   Tue, 14 Nov 2017 22:09:34 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     Petr Mladek <pmladek@...e.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [GIT pull] printk updates for 4.15

On Tue, 14 Nov 2017, Linus Torvalds wrote:
> On Tue, Nov 14, 2017 at 12:21 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > First of all sched_clock() and CLOCK_MONOTONIC can drift apart frequency
> > wise pretty bad.
> 
> Yes. And I would actuall ynot object to just making the printk buffers
> use CLOCK_MONOTONIC.
> 
> The reason we avoided that was we didn't want to take the locks, though.

I know, but today we can use the NMI safe accessor which avoids that.

> sched_clock() is used not because it's the right clock, or
> particularly good, but because it is fast and doesn't have locking
> issues.
> 
> But all of this is entirely separate from the "changing from one clock
> that has small issues for good reasons to FOUR DIFFERENT CLOCKS THAT
> THE USER CHOOSES RANDOMLY".
> 
> See my objection?

I understand that and I certainly was not trying to argue about that.

Thanks,

	tglx