Jeremy Chadwick wrote on 10/29/2015 11:09:
On Thu, Oct 29, 2015 at 11:00:32AM +0100, Miroslav Lachman wrote:
Jeremy Chadwick wrote on 10/27/2015 06:05:
(I am not subscribed to the mailing list, please keep me CC'd)
Issue: a stable/10 system that has an abnormally high load average (e.g.
0.15, but may be higher depending on other variables which I can't
account for) when the machine is definitely idle (i.e. cannot be traced
to high interrupt usage per vmstat -i, cannot be traced to a userland
process or kernel thread, etc.).
This problem has been discussed many times on the FreeBSD mailing lists
and the FreeBSD forum (including some folks seeing it on 9.x, but my
complaint here is focused on 10.x so please focus there).
I'd politely like to request that anyone experiencing this, or who has
experienced it (and if you know when it stopped or why, including what
you may have done, include that), to chime in on this ticket from 2012
(made for 9.x but style of issue still applies; c#5 is quite valid):
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=173541
For those still experiencing it, I'd suggest reading c#8 and seeing if
sysctl kern.eventtimer.periodic=1 relieves the problem for you. (At
this time I would not suggest leaving that set indefinitely, as it does
seem to increase the interrupt rate in cpuX:timer in vmstat -i. But for
me kern.eventtimer.periodic=1 "fixes" the issue)
Is it on real HW server or in some kind of virtualization? I am seeing load
0.5 - 1.2 on three virtual machines in VMware. The machines are without any
traffic. Just fresh instalation of FreeBSD 10.1 and some services without
any public content.
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
Miroslav Lachman
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