On Sun, Jun 16, 2013 at 07:53:41PM +0100, Sami Kerola wrote:
> Unfortunately the most troubling dmesg patch is now dropped by me. I had
> a look how systemd determines boot time, and it seem very early at
> execution clock_gettime() is called, and results are saved. If dmesg
> should agree with systemd when startup happen I see two possible options;
>
> 1. Make dmesg to get system startup time from systemd using dbus.
>
> 2. Make both dmesg and systemd to ask start up time from kernel.
>
> I feel first option is not great. The systemd boot time stamp is similar
> sort of approximation as reading fstat from /proc/1. Also asking when
> system started from system itself feels more neutral than consulting a
> software the system started.
>
> If the second option is favored a kernel patch, such as the one below, is
> needed and a bit coordination to make various programs to use the
> boottime from kernel. Meanwhile it migth be fine that differnt programs
> using differnet time stamps for klog messages.
Note that the current dmesg(1) code uses sysinfo(2) which provides
uptime in seconds. It would be probably better to use /proc/uptime
where is uptime in sec.xx precision.
> Any opinions about klog time stamps?
>
>
> --- a/kernel/ksysfs.c
> +++ b/kernel/ksysfs.c
> @@ -157,6 +157,16 @@ static ssize_t rcu_expedited_store(struct kobject
> *kobj,
> }
> KERNEL_ATTR_RW(rcu_expedited);
>
> +/* High precision timestamp of the system boot. */
> +static ssize_t boottime_show(struct kobject *kobj,
> + struct kobj_attribute *attr, char *buf)
> +{
> + struct timespec ts;
> + getboottime(&ts);
> + return sprintf(buf, "%ld.%ld\n", ts.tv_sec, ts.tv_nsec);
> +}
> +KERNEL_ATTR_RO(hp_uptime);
> +
> /*
> * Make /sys/kernel/notes give the raw contents of our kernel .notes
> * section.
> */
> @@ -197,6 +207,7 @@ static struct attribute * kernel_attrs[] = {
> &vmcoreinfo_attr.attr,
> #endif
> &rcu_expedited_attr.attr,
> + &hp_uptime_attr.attr,
> NULL
> };
Would be better to use /proc (where is 'uptime' file) rather than
/sys/kernel ?
Karel
--
Karel Zak <kzak@xxxxxxxxxx>
http://karelzak.blogspot.com
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