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List:       openbsd-bugs
Subject:    Re: Degraded timing performance - QEMU, KVM - OpenBSD 6.2
From:       Mike Larkin <mlarkin () azathoth ! net>
Date:       2017-12-26 19:36:28
Message-ID: 20171226193628.GI29519 () azathoth ! net
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On Tue, Dec 26, 2017 at 12:27:31PM -0500, Andrew Davis wrote:
> Hello,
> 
> I'm experiencing some odd timing issues on OpenBSD 6.2 (and 6.1) on the
> system listed below. This is preventing me from running OpenBSD on my
> servers. Can you determine if this is a bug in the OpenBSD operating system?
> I can provide more information if needed.
> 
> Virtualized environment.
> 
> Host CPU: 2 x Intel E5-2630 v3 2.4 Ghz
> Host OS: Fedora 27
> Virtualization software: QEMU + KVM (2.10.0-1.fc27)
> Guest Machine: default (pc-i440fx-2.10)
> Guest OS: OpenBSD 6.2 (and 6.1).
> 
> Basically, OpenBSD processes degrade over time to the point where they're
> completely unresponsive. This simple date printout script is a good example.
> It should print out the date once per second, but after roughly ~20 mins on
> this hardware configuration, it takes 2 seconds to print each line, then 4
> seconds to print each line, and so on. After running for about 24 hours, the
> delay is about 1 minute between line printouts.
> 
>     while sleep 1; do date; done
> 
> I've tried tweaking some different settings on the guest and host, such as
> disabling the HPET timer and x2apic, neither of which has proven effective.
> 
> I saw mention of adding "kvm-intel.preemption_timer=0" in another recent
> thread. This seems to resolve the slowdown issue.
> 
> However, I have run other guest operating systems on this hardware
> configuration (CentOS, Ubuntu, FreeBSD) - neither of which required any of
> these tweaks, or experienced timing issues. This leads me to believe that it
> could be related to a bug in OpenBSD.
> 
> I have access to several machines with this hardware configuration and
> tested on multiple machines, to rule out a possible one-off hardware issue.
> Each host displayed the same behavior.
> 
> Best regards,
> Andrew
> 

What timecounter source did the OpenBSD guests pick? Did you try selecting
one of the other choices to see if this helps?

sysctl kern.timecounter    if you're not sure what I'm talking about.

-ml

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