Re: [PATCH 8/9] per-cgroup boot time

[Glauber Costa]

On 09/20/2011 10:04 AM, Peter Zijlstra wrote:
> On Tue, 2011-09-20 at 09:37 -0300, Glauber Costa wrote:
>
> > > > +	getboottime(&boottime);
> > > > +	ts = timespec_add(boottime, ca->start_time);
> > > > +	jif = ts.tv_sec;
> > > >
> > > >    	for_each_possible_cpu(i) {
> > > >    		cpustat = per_cpu_ptr(ca->cpustat, i);
> > >
> > >
> > > I'm confused, what does it do? You take a boot time timestamp at cgroup
> > > creation, add that to all boot-time readings and print the result. How
> > > does that make sense? Subtracting the start_time, maybe, that would make
> > > the cgroup creation time 0, adding, not so much.
> >
> > Boot time represent at which times the machine was booted. In this
> > context, at which time the container/cgroup was created. So it have to
> > be an addition.... don't really understand your question
>
> I think we're all properly confused now :-)
>
> getboottime() gives a time since boot, right?
>
> You take stamp at cgroup creation: say 50s after boot.
>
> Then on usage you take a new getboottime() reading (which per definition
> is>  50s) and add your 50s that you read previous. This results in the
> cgroup having 50s of boot-time _MORE_ than the machine. Say you read at
> 123s, you then add your 50s timestamp, resulting in 173s to report.
>
> If instead you did a subtraction: 123-50=73, you would have reported the
> time since cgroup creation.
no.

/**
 * getboottime - Return the real time of system boot.
 * @ts:         pointer to the timespec to be set
 *
 * Returns the wall-time of boot in a timespec.
...
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