From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: "Alex Ng \(LIS\)" <alexng@microsoft.com>
Cc: "devel\@linuxdriverproject.org" <devel@linuxdriverproject.org>,
"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"KY Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
"John Stultz" <john.stultz@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 3/4] hv_util: use do_adjtimex() to update system time
Date: Tue, 03 Jan 2017 13:32:22 +0100 [thread overview]
Message-ID: <87a8b8qq7d.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <MWHPR03MB2734B2657BA19D402C0ED1A6D86F0@MWHPR03MB2734.namprd03.prod.outlook.com> (Alex Ng's message of "Mon, 2 Jan 2017 23:24:38 +0000")
"Alex Ng (LIS)" <alexng@microsoft.com> writes:
>> -----Original Message-----
>> From: Vitaly Kuznetsov [mailto:vkuznets@redhat.com]
>> Sent: Monday, January 2, 2017 11:41 AM
>> To: devel@linuxdriverproject.org
>> Cc: linux-kernel@vger.kernel.org; KY Srinivasan <kys@microsoft.com>;
>> Haiyang Zhang <haiyangz@microsoft.com>; John Stultz
>> <john.stultz@linaro.org>; Thomas Gleixner <tglx@linutronix.de>; Alex Ng
>> (LIS) <alexng@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 <vkuznets@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
next prev parent reply other threads:[~2017-01-03 12:32 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-02 19:41 [PATCH 0/4] hv_util: adjust system time smoothly Vitaly Kuznetsov
2017-01-02 19:41 ` [PATCH 1/4] timekeeping: export do_adjtimex() to modules Vitaly Kuznetsov
2017-01-02 19:41 ` [PATCH 2/4] hv_util: switch to using timespec64 Vitaly Kuznetsov
2017-01-02 19:41 ` [PATCH 3/4] hv_util: use do_adjtimex() to update system time Vitaly Kuznetsov
2017-01-02 23:24 ` Alex Ng (LIS)
2017-01-03 12:32 ` Vitaly Kuznetsov [this message]
2017-01-03 19:48 ` Alex Ng (LIS)
2017-01-09 17:19 ` Stephen Hemminger
2017-01-09 17:40 ` Vitaly Kuznetsov
2017-01-09 17:58 ` Stephen Hemminger
2017-01-09 18:14 ` Vitaly Kuznetsov
2017-01-09 18:31 ` Stephen Hemminger
2017-01-02 19:41 ` [PATCH 4/4] hv_util: improve time adjustment accuracy by disabling interrupts Vitaly Kuznetsov
2017-01-02 19:50 ` Stephen Hemminger
2017-01-03 12:28 ` Vitaly Kuznetsov
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