Sorry for the delay.
I'm using Armbian 5.75 Stable (Stretch)
$ uname -a
Linux pine64 4.20.7-sunxi64 #5.75 SMP Fri Feb 8 10:37:18 CET 2019 aarch64 GNU/Linux
I'll try with the nightly build on 5.x and check if it works.
Also, here's Andre's test_timer output:
# ./timer
TAP version 13
# number of cores: 4
ok 1 same timer frequency on all cores
# timer frequency is 24000000 Hz (24 MHz)
# time1: a33e3cbff, time2: a33e3c80b, diff: -1012
# time1: a33e533ff, time2: a33e5300b, diff: -1012
# time1: a33ea87f5, time2: a33ea8400, diff: -1013
# time1: a33eb4bff, time2: a33eb480b, diff: -1012
# time1: a33f6b7f4, time2: a33f6b400, diff: -1012
# time1: a341037f4, time2: a34103400, diff: -1012
# time1: a34233ff5, time2: a34230c00, diff: -13301
# time1: a342ccff4, time2: a342ccc00, diff: -1012
# time1: a342edff5, time2: a342ed3ff, diff: -3062
# time1: a3430d7f5, time2: a3430d400, diff: -1013
# time1: a3436d7f4, time2: a3436d400, diff: -1012
# time1: a343a83ff, time2: a343a8014, diff: -1003
# time1: a343c17f5, time2: a343c1400, diff: -1013
# time1: a34568bff, time2: a3456880b, diff: -1012
# time1: a345e2c00, time2: a345e200b, diff: -3061
# time1: a3465b7f5, time2: a3465b400, diff: -1013
# too many errors, stopping reports
not ok 2 native counter reads are monotonic # 370 errors
# min: -15350, avg: 11, max: 15372
# diffs: -127209, -41834, -127167, -41834, -41792, -41834, -41834, -41792, -41833, -41834, -41792, -41834, -41792, -41833, -41834, -127250
# too many errors, stopping reports
not ok 3 Linux counter reads are monotonic # 373 errors
# min: -174633417, avg: 807, max: 640875
# core 0: counter value: 44453336039 => 1852 sec
# core 0: offsets: back-to-back: 15, b-t-b synced: 12, b-t-b w/ delay: 20
# core 1: counter value: 44453431859 => 1852 sec
# core 1: offsets: back-to-back: 12, b-t-b synced: 11, b-t-b w/ delay: 15
# core 2: counter value: 44453624827 => 1852 sec
# core 2: offsets: back-to-back: 19, b-t-b synced: 12, b-t-b w/ delay: 20
# core 3: counter value: 44453630152 => 1852 sec
# core 3: offsets: back-to-back: 13, b-t-b synced: 12, b-t-b w/ delay: 19
1..3
