Messages in this thread | | | Subject | Re: [PATCH 8/9] per-cgroup boot time | From | Peter Zijlstra <> | Date | Tue, 20 Sep 2011 15:04:20 +0200 |
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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.
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