stable/10: high load average when box is idle

[Miroslav Lachman]

Miroslav Lachman wrote on 10/29/2015 12:47:
> Jeremy Chadwick wrote on 10/29/2015 11:09:

[...]

>> I've seen it on both bare-metal and VMs.  Please see c#8 in the ticket;
>> there's an itemised list of where I've seen it, but I'm sure it's not
>> limited to just those.
>
> OK, I have read your c#8 and did some tests on our affected VMs.
> With sysctl kern.eventtimer.periodic=1 it is better. Where previously
> load were about 0.40 is 0.15 now.
> One of these three systems is FreeBSD 10.2 and on this machine the
> positive effect of kern.eventtimer.periodic=1 is more visible - load is
> now 0.00 - 0.05.
> I don't know if this is some coincidence or something is different in 10.2.
>
> Settings of kern.eventtimer is the same on all VMs
>
> kern.eventtimer.et.LAPIC.flags: 7
> kern.eventtimer.et.LAPIC.frequency: 35071418
> kern.eventtimer.et.LAPIC.quality: 600
> kern.eventtimer.et.i8254.flags: 1
> kern.eventtimer.et.i8254.frequency: 1193182
> kern.eventtimer.et.i8254.quality: 100
> kern.eventtimer.et.RTC.flags: 17
> kern.eventtimer.et.RTC.frequency: 32768
> kern.eventtimer.et.RTC.quality: 0
> kern.eventtimer.choice: LAPIC(600) i8254(100) RTC(0)
> kern.eventtimer.singlemul: 4
> kern.eventtimer.idletick: 0
> kern.eventtimer.timer: LAPIC
> kern.eventtimer.periodic: 1


Just for the record - I added graphs of CPU load from these three VMs

FreeBSD 10.1
http://imagebin.ca/v/2Kkyq29M13d3
FreeBSD 10.1
http://imagebin.ca/v/2KkzUccxJEoE
FreeBSD 10.2
http://imagebin.ca/v/2Kl00mS4RQ3n

And coresponding CPU idle percentages

FreeBSD 10.1
http://imagebin.ca/v/2Kl0R0U1pRhg
FreeBSD 10.1
http://imagebin.ca/v/2Kl0cYiB0mS4
FreeBSD 10.2
http://imagebin.ca/v/2Kl0lIipTKXc

As I mentioned the difference with / without kern.eventtimer.periodic=1 
is more visible on FreeBSD 10.2.

The flat line on the graphs is interval where I disabled almost all 
services - crontab too - so no measurements in this time.
Effect of kern.eventtimer.periodic=1 is visible from 18:00 when I 
started all usual services.

Miroslav Lachman