Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx> writes:
> On Wed, 4 Jan 2017 18:24:38 +0100
> Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote:
>
>> 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.
>>
>> Instead of calling do_settimeofday64() we can pretend being an NTP client
>> and use do_adjtimex(). Do do_settimeofday64() in case the difference is too
>> big or ICTIMESYNCFLAG_SYNC flag was set in the request.
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
>> ---
>> 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)
>> ---
>> drivers/hv/hv_util.c | 32 +++++++++++++++++++++++++++++---
>> 1 file changed, 29 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c
>> index 94719eb..7e97231 100644
>> --- a/drivers/hv/hv_util.c
>> +++ b/drivers/hv/hv_util.c
>> @@ -182,9 +182,11 @@ struct adj_time_work {
>> static void hv_set_host_time(struct work_struct *work)
>> {
>> struct adj_time_work *wrk;
>> - s64 host_tns;
>> + s64 host_tns, our_tns, delta;
>> u64 newtime;
>> - struct timespec64 host_ts;
>> + struct timespec64 host_ts, our_ts;
>> + struct timex txc = {0};
>> + int ret;
>>
>> wrk = container_of(work, struct adj_time_work, work);
>>
>> @@ -205,7 +207,31 @@ static void hv_set_host_time(struct work_struct *work)
>> host_tns = (newtime - WLTIMEDELTA) * 100;
>> host_ts = ns_to_timespec64(host_tns);
>>
>> - do_settimeofday64(&host_ts);
>> + getnstimeofday64(&our_ts);
>> + our_tns = timespec64_to_ns(&our_ts);
>> +
>> + /* Difference between our time and host time */
>> + delta = host_tns - our_tns;
>
> This looks correct to me.
> Did you consider using ktime? It provides a cleaner abstraction for handling
> nanosecond time resolution.
I see. While s64 should work ktime seems preferable. I'll give it a try.
--
Vitaly
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