[Bug 256781] TSC-low timecounter lags on EC2 nitro instances

From: <bugzilla-noreply_at_freebsd.org>
Date: Tue, 22 Jun 2021 19:04:34 +0000
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=256781

            Bug ID: 256781
           Summary: TSC-low timecounter lags on EC2 nitro instances
           Product: Base System
           Version: 13.0-RELEASE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: bugs_at_FreeBSD.org
          Reporter: martin.stoyanov_at_vertalo.com

I am trying to use the latest FreeBSD 13 Release AMIs on EC2 and by default
they start up with:
kern.timecounter.hardware: TSC-low
which results in a very slow clock. I did these rudimentary tests, hopefully
demonstrating the problem. (all date commands were executed one minute apart
after switching the timecounter.

root_at_buildbot_master: # sysctl kern.timecounter.hardware=i8254
kern.timecounter.hardware: TSC-low -> i8254
root_at_buildbot_master: # date
Tue Jun 22 18:22:45 UTC 2021
root_at_buildbot_master: # date
Tue Jun 22 18:23:46 UTC 2021

root_at_buildbot_master: # sysctl kern.timecounter.hardware=ACPI-fast
kern.timecounter.hardware: i8254 -> ACPI-fast
root_at_buildbot_master: # date
Tue Jun 22 18:24:46 UTC 2021
root_at_buildbot_master: # date
Tue Jun 22 18:25:45 UTC 2021

root_at_buildbot_master: # sysctl kern.timecounter.hardware=HPET
kern.timecounter.hardware: ACPI-fast -> HPET
root_at_buildbot_master: # date
Tue Jun 22 18:26:45 UTC 2021
root_at_buildbot_master: # date
Tue Jun 22 18:27:45 UTC 2021

root_at_buildbot_master:/var/service-dir # sysctl
kern.timecounter.hardware=TSC-low
kern.timecounter.hardware: HPET -> TSC-low
root_at_buildbot_master: # date
Tue Jun 22 18:28:16 UTC 2021
root_at_buildbot_master: # date
Tue Jun 22 18:28:43 UTC 2021

This is the uname of the machine and if you need any additional info I'd be
happy to provide it:
root_at_buildbot_master: # uname -a
FreeBSD buildbot_master 13.0-RELEASE-p1 FreeBSD 13.0-RELEASE-p1 #0: Wed May 26
22:15:09 UTC 2021    
root_at_amd64-builder.daemonology.net:/usr/obj/usr/src/amd64.amd64/sys/GENERIC 
amd64

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Received on Tue Jun 22 2021 - 19:04:34 UTC

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