[Bug 256781] EC2 Nitro: TSC-low timecounter lags

From: <bugzilla-noreply_at_freebsd.org>
Date: Mon, 13 Sep 2021 16:11:54 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=256781

--- Comment #32 from martin.stoyanov@vertalo.com ---
(In reply to Colin Percival from comment #30)
I guess I spoke too soon - after a reboot of this instance, this is what I get
(with TSC-low):

root@freebsd:~ # uname -a
FreeBSD freebsd 14.0-CURRENT FreeBSD 14.0-CURRENT #0 main-n249319-3a0976dea38:
Sun Sep 12 14:01:34 UTC 2021    
root@freebsd:/usr/obj/usr/src/amd64.amd64/sys/GENERIC  amd64
root@freebsd:~ # sysctl kern.timecounter
kern.timecounter.tsc_shift: 1
kern.timecounter.smp_tsc_adjust: 0
kern.timecounter.smp_tsc: 1
kern.timecounter.invariant_tsc: 1
kern.timecounter.fast_gettime: 1
kern.timecounter.tick: 1
kern.timecounter.choice: i8254(0) ACPI-fast(900) HPET(950) kvmclock(975)
TSC-low(1000) dummy(-1000000)
kern.timecounter.hardware: TSC-low
kern.timecounter.alloweddeviation: 5
kern.timecounter.timehands_count: 2
kern.timecounter.stepwarnings: 0
kern.timecounter.tc.i8254.quality: 0
kern.timecounter.tc.i8254.frequency: 1193182
kern.timecounter.tc.i8254.counter: 24651
kern.timecounter.tc.i8254.mask: 65535
kern.timecounter.tc.ACPI-fast.quality: 900
kern.timecounter.tc.ACPI-fast.frequency: 3579545
kern.timecounter.tc.ACPI-fast.counter: 3169760
kern.timecounter.tc.ACPI-fast.mask: 16777215
kern.timecounter.tc.HPET.quality: 950
kern.timecounter.tc.HPET.frequency: 62500000
kern.timecounter.tc.HPET.counter: 163922095
kern.timecounter.tc.HPET.mask: 4294967295
kern.timecounter.tc.kvmclock.quality: 975
kern.timecounter.tc.kvmclock.frequency: 1000000000
kern.timecounter.tc.kvmclock.counter: 236796286
kern.timecounter.tc.kvmclock.mask: 4294967295
kern.timecounter.tc.TSC-low.quality: 1000
kern.timecounter.tc.TSC-low.frequency: 1244790063
kern.timecounter.tc.TSC-low.counter: 1383859311
kern.timecounter.tc.TSC-low.mask: 4294967295
root@freebsd:~ # date ; sntp pool.ntp.org ; sleep 60 ; date ; sntp pool.ntp.org
Mon Sep 13 15:45:25 UTC 2021
ntpd 4.2.8p15-a (1)
kod_init_kod_db(): Cannot open KoD db file /var/db/ntp-kod: No such file or
directory
2021-09-13 15:45:25.093618 (+0000) +194.309232 +/- 129.554879 pool.ntp.org
23.131.160.7 s2 no-leap
Mon Sep 13 15:46:25 UTC 2021
ntpd 4.2.8p15-a (1)
kod_init_kod_db(): Cannot open KoD db file /var/db/ntp-kod: No such file or
directory
2021-09-13 15:46:25.245602 (+0000) +270.24435 +/- 180.186988 pool.ntp.org
83.68.137.76 s2 no-leap

and with KVMCLOCK:

root@freebsd:~ # sysctl kern.timecounter
kern.timecounter.tsc_shift: 1
kern.timecounter.smp_tsc_adjust: 0
kern.timecounter.smp_tsc: 1
kern.timecounter.invariant_tsc: 1
kern.timecounter.fast_gettime: 1
kern.timecounter.tick: 1
kern.timecounter.choice: i8254(0) ACPI-fast(900) HPET(950) kvmclock(975)
TSC-low(1000) dummy(-1000000)
kern.timecounter.hardware: kvmclock
kern.timecounter.alloweddeviation: 5
kern.timecounter.timehands_count: 2
kern.timecounter.stepwarnings: 0
kern.timecounter.tc.i8254.quality: 0
kern.timecounter.tc.i8254.frequency: 1193182
kern.timecounter.tc.i8254.counter: 33596
kern.timecounter.tc.i8254.mask: 65535
kern.timecounter.tc.ACPI-fast.quality: 900
kern.timecounter.tc.ACPI-fast.frequency: 3579545
kern.timecounter.tc.ACPI-fast.counter: 10497046
kern.timecounter.tc.ACPI-fast.mask: 16777215
kern.timecounter.tc.HPET.quality: 950
kern.timecounter.tc.HPET.frequency: 62500000
kern.timecounter.tc.HPET.counter: 2364450388
kern.timecounter.tc.HPET.mask: 4294967295
kern.timecounter.tc.kvmclock.quality: 975
kern.timecounter.tc.kvmclock.frequency: 1000000000
kern.timecounter.tc.kvmclock.counter: 1123025369
kern.timecounter.tc.kvmclock.mask: 4294967295
kern.timecounter.tc.TSC-low.quality: 1000
kern.timecounter.tc.TSC-low.frequency: 1244790063
kern.timecounter.tc.TSC-low.counter: 3561554254
kern.timecounter.tc.TSC-low.mask: 4294967295
root@freebsd:~ # date ; sntp pool.ntp.org ; sleep 60 ; date ; sntp pool.ntp.org
Mon Sep 13 16:06:29 UTC 2021
ntpd 4.2.8p15-a (1)
kod_init_kod_db(): Cannot open KoD db file /var/db/ntp-kod: No such file or
directory
2021-09-13 16:06:29.878712 (+0000) -0.420875 +/- 0.322316 pool.ntp.org
72.30.35.88 s2 no-leap
Mon Sep 13 16:07:29 UTC 2021
ntpd 4.2.8p15-a (1)
kod_init_kod_db(): Cannot open KoD db file /var/db/ntp-kod: No such file or
directory
2021-09-13 16:07:29.984987 (+0000) -0.422455 +/- 0.334305 pool.ntp.org
168.235.86.33 s2 no-leap


I can keep that instance up and give you access if you want...

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