Re: Question about /proc/uptime
From: Martin Schwidefsky
Date: Thu Jan 02 2014 - 03:28:35 EST
On Wed, 01 Jan 2014 15:21:00 -0600
Rob Landley <rob@xxxxxxxxxxx> wrote:
> On 01/01/14 06:41, Martin Schwidefsky wrote:
> > On Tue, 31 Dec 2013 22:17:39 -0600
> > Rob Landley <rob@xxxxxxxxxxx> wrote:
> >> On 12/30/13 09:26, Martin Schwidefsky wrote:
> >>> On Mon, 30 Dec 2013 16:11:10 +0100
> >>> Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> >>>> Not sure I understand... except that timekeeping_resume() does
> >>>> __timekeeping_inject_sleeptime().
> >>> Hmm, you are right. The sleeptime is added to the monotonic boottime.
> >>> So the first value of /proc/uptime is the wall-time since boot.
> >>> And the second value is combined idle time over all cpus.
> >> Is there an obvious way to query the non-suspend uptime from userspace?
> > clock_gettime with CLOCK_MONOTONIC gives you the uptime minus without the
> > suspend time.
> Given that the clock_gettime man page says:
> Clock that cannot be set and represents monotonic time since
> some unspecified starting point.
> Can I rely on it _continuing_ to do so in future, and if so should the
> man page be clarified?
Good point. CLOCK_MONOTONIC is implemented in a specific way now and I
doubt that this will change any time soon, but you have no guarantee that
it will keep the property 'monotonic-time = uptime - suspend-time'.
You can not use the values in /proc/stat either as you can set any CPU
offline, which means that no CPU line contains all ticks since boot.
Without the CLOCK_MONOTONIC option I do not see a way how to get the
non-suspend uptime from user space.
"Reality continues to ruin my life." - Calvin.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/