Messages in this thread | | | From | Vitaly Kuznetsov <> | Subject | [PATCH v2 0/4] hv_util: adjust system time smoothly | Date | Wed, 4 Jan 2017 18:24:35 +0100 |
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Changes since v1: - do do_settimeofday64() when ICTIMESYNCFLAG_SYNC flag is present in the request (Alex Ng) - add pr_debug() for the case when do_adjtimex() fails (Alex Ng)
Original description:
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 | 40 ++++++++++++++++++++++++++++++++++++---- kernel/time/timekeeping.c | 1 + 2 files changed, 37 insertions(+), 4 deletions(-)
-- 2.9.3
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