Messages in this thread | | | Date | Thu, 2 Jan 2014 09:28:23 +0100 | From | Martin Schwidefsky <> | Subject | Re: Question about /proc/uptime |
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On Wed, 01 Jan 2014 15:21:00 -0600 Rob Landley <rob@landley.net> wrote:
> On 01/01/14 06:41, Martin Schwidefsky wrote: > > On Tue, 31 Dec 2013 22:17:39 -0600 > > Rob Landley <rob@landley.net> wrote: > > > >> On 12/30/13 09:26, Martin Schwidefsky wrote: > >>> On Mon, 30 Dec 2013 16:11:10 +0100 > >>> Oleg Nesterov <oleg@redhat.com> 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_MONOTONIC > 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.
-- blue skies, Martin.
"Reality continues to ruin my life." - Calvin.
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