Monitoring CPU time

[Stuart Nelson]

Excellent, thank you!

On Mon, Sep 19, 2016 at 3:38 AM Sepherosa Ziehau <sepherosa at gmail.com>
wrote:

> Hi,
>
> The bump upon each statclock is:
> ((cur_systimer - prev_systimer) * systimer_freq) >> 32
>
> systimer_freq can be extracted from following sysctl in userspace:
> sysctl kern.cputimer.freq
>
> statclock is called at stathz frequency.
>
> Thanks,
> sephe
>
>
> On Mon, Sep 19, 2016 at 12:46 AM, Stuart Nelson <stuartnelson3 at gmail.com>
> wrote:
> > Hey all,
> >
> > I'm following up on some work from this old thread for monitoring CPU
> time:
> > https://www.dragonflybsd.org/mailarchive/users/2010-04/msg00056.html
> >
> > The code I have is essentially the one shown in the link, but I'm
> attempting
> > to find the actual number of seconds spent in each state. I'm doing this
> by
> > dividing each value by clockrate.stathz, e.g.:
> >
> >
> > user += cp_t[cpu].cp_user / clockrate.stathz;
> >
> >
> > Relevant code is here:
> >
> https://github.com/stuartnelson3/node_exporter/blob/2b5a581942ac31b501438d402274100df1f7d3d6/collector/cpu_dragonfly.go#L50-L98
> >
> > My question is about the units on struct members in kinfo_cputime (the
> > source of cp_user et al.). The values I'm getting out seem to be growing
> at
> > a rate that indicates I'm not looking at seconds, but something smaller.
> >
> > I'm looking at the rate of change of cpu time on my personal machine
> running
> > dragonfly vs. a machine running linux. The implementation is the same:
> get
> > user time, divide by 100Hz to get the value in seconds, and find the
> rate of
> > change between two collections in fixed time window. The dragonfly rate
> of
> > change seems to be larger by about 2 orders of magnitude, which is why
> I'm
> > asking about the units.
> >
> > For reference, the dragonfly node I'm looking at is reporting ~200
> increase
> > per second in cpu time for user and sys with loadavg ~0.1%, whereas the
> > linux node is reporting values <10 with loadavg ~15%.
> >
> > I'm improving dragonfly support for the node_exporter for Prometheus, a
> > metrics and monitoring solution that is used mostly in the linux
> community.
> > I'm assuming the linux implementation for finding cpu time in seconds is
> > correct, and it's also the implementation used for finding cpu seconds
> for
> > freebsd. It just struck me as unlikely that my old dell running dragonfly
> > would have a rate of change at a fraction of the load that was so
> > drastically different.
> >
> > If there is anything I can clarify don't hesitate to write back!
> >
> > Thanks,
> > Stuart
> >
> >
>
>
>
> --
> Tomorrow Will Never Die
>
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