"Alex Ng (LIS)" <ale...@microsoft.com> writes:
>> -----Original Message-----
>> From: Vitaly Kuznetsov [mailto:vkuzn...@redhat.com]
>> Sent: Monday, January 2, 2017 11:41 AM
>> To: de...@linuxdriverproject.org
>> Cc: linux-kernel@vger.kernel.org; KY Srinivasan <k...@microsoft.com>;
>> Haiyang Zhang <haiya...@microsoft.com>; John Stultz
>> <john.stu...@linaro.org>; Thomas Gleixner <t...@linutronix.de>; Alex Ng
>> (LIS) <ale...@microsoft.com>
>> Subject: [PATCH 3/4] hv_util: use do_adjtimex() to update system time
>>
>> 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.
>
> These are all good points. I am working on a patch to address point 2.
> It will allow new TimeSync behavior to be disabled even if the TimeSync IC is
> enabled from the host. This can be set to prevent TimeSync IC from interfering
> with NTP client.
>
Good, this can happen in parallel to my series, right?
>>
>> Instead of calling do_settimeofday64() we can pretend being an NTP client
>> and use do_adjtimex().
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
>> ---
>> drivers/hv/hv_util.c | 25 ++++++++++++++++++++++---
>> 1 file changed, 22 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c index
>> 94719eb..4c0fbb0 100644
>> --- a/drivers/hv/hv_util.c
>> +++ b/drivers/hv/hv_util.c
>> @@ -182,9 +182,10 @@ 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};
>>
>> wrk = container_of(work, struct adj_time_work, work);
>>
>> @@ -205,7 +206,25 @@ 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;
>> +
>> + /* Try adjusting time by using phase adjustment if possible */
>> + if (abs(delta) > MAXPHASE) {
>> + do_settimeofday64(&host_ts);
>> + return;
>> + }
>
> We should also call do_settimeofday64() if the host sends flag
> ICTIMESYNCFLAG_SYNC. This is a signal from host that the guest
> shall sync with host time immediately (often when the guest has
> just booted).
Ok, point taken, will do in v2. We don't get ICTIMESYNCFLAG_SYNC very
often, right?
>
>> +
>> + txc.modes = ADJ_TICK | ADJ_FREQUENCY | ADJ_OFFSET |
>> ADJ_NANO |
>> + ADJ_STATUS;
>> + txc.tick = TICK_USEC;
>> + txc.freq = 0;
>
> I'm not familiar with the ADJ_FREQUENCY flag. What does setting this to
> 'zero' achieve?
> Are there any side-effects from doing this?
Zero means no frequency adjustment required (we reset it in case it was
previously made by an NTP client).
>
>> + txc.status = STA_PLL;
>> + txc.offset = delta;
>> + do_adjtimex(&txc);
>
> Might be a good idea to handle the return code from do_adjtimex() and log
> something
> in case of error.
I can add a debug message here but as this is a regular action we don't
want to get a flood of messages in case this fails permanently. I'd
avoid printing info messages here.
>
>> }
>>
>> /*
>> --
>> 2.9.3
--
Vitaly
