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Subject[PATCH 0/4] hv_util: adjust system time smoothly
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(First, I have to admit I'm not a timekeeping expert ...)

With TimeSync version 4 protocol support we started updating system time
continuously through the whole lifetime of Hyper-V guests. Every 5 seconds
there is a time sample from the host which triggers do_settimeofday[64]().
While the time from the host is very accurate such adjustments may cause
issues:
- Time is jumping forward and backward, some applications may misbehave.
- In case an NTP client is run in parallel things may go south, e.g. when
an NTP client tries to adjust tick/frequency with ADJ_TICK/ADJ_FREQUENCY
the Hyper-V module will not see this changes and time will oscillate and
never converge.
- Systemd starts annoying you by printing "Time has been changed" every 5
seconds to the system log.

With this series I suggest to use do_adjtimex() to adjust time. My tests
show that such method gives equally good time convergence but avoids all
the drawbacks described above.

Vitaly Kuznetsov (4):
timekeeping: export do_adjtimex() to modules
hv_util: switch to using timespec64
hv_util: use do_adjtimex() to update system time
hv_util: improve time adjustment accuracy by disabling interrupts

drivers/hv/hv_util.c | 33 +++++++++++++++++++++++++++++----
kernel/time/timekeeping.c | 1 +
2 files changed, 30 insertions(+), 4 deletions(-)

--
2.9.3

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