linux-kernel - Re: [PATCH] proc: make high precision system boot time available

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Message-ID: <CAG27Bk33MbFsbxz7QxApw5i0eGJaPc2Mf2UgcL0rqLNcty4HCQ@mail.gmail.com>
Date:	Sun, 30 Jun 2013 18:46:34 +0100
From:	Sami Kerola <kerolasa@....fi>
To:	Kay Sievers <kay@...y.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, Karel Zak <kzak@...hat.com>,
	Lennart Poettering <lennart@...ttering.net>
Subject: Re: [PATCH] proc: make high precision system boot time available

On 30 June 2013 16:10, Kay Sievers <kay@...y.org> wrote:
> On Sat, Jun 29, 2013 at 10:53 PM, Sami Kerola <kerolasa@....fi> wrote:
>
>> BTW having a way to measure effect of suspend/resume could lead to a
>> way to fix time time distortion.
>
>> Perhaps there is better alternative to fix user space programs.
>> Unfortunately I do not have either knowledge, or imagination, to come
>> up with any. Fix hints, ideas, and other proposal are most welcome.
>
> Stuff should just use:
>   clock_gettime(CLOCK_BOOTTIME, &ts);
>
> to get the time in better resolution, and with suspend time taken into account?
>
> As a general note, the kmsg/printk() time in the raw kernel log is the
> time of the CPU it runs on, especially during early init this time
> might not be in sync across CPUs and stuff jumps event in the very
> same stream on events from the kernel itself:
>   http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/kernel/sched/clock.c#n329

Thank you Kay,

The clock_gettime(CLOCK_BOOTTIME, &uptime); seems to be exactly what
dmesg needs. A patch to fix dmesg wigging will be sent to util-linux
maillist shortly. Perhaps the dmesg / journald time stamp difference
issue will be fixed someday, but that discussion does not belong to
linux-kernel mailist, so it is time to declare

end of thread.

--
Sami Kerola
http://www.iki.fi/kerolasa/
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