linux-kernel - [PATCH v4 0/2] hv_util: adjust system time smoothly

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Date:   Thu, 19 Jan 2017 15:16:34 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     devel@...uxdriverproject.org
Cc:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        John Stultz <john.stultz@...aro.org>,
        Alex Ng <alexng@...rosoft.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Olaf Hering <olaf@...fle.de>,
        Richard Cochran <richardcochran@...il.com>,
        Radim Krcmar <rkrcmar@...hat.com>
Subject: [PATCH v4 0/2] hv_util: adjust system time smoothly

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 server runs in parallel and uses something else for time
  sync (network, PTP,...) system time will never converge.
- Systemd starts annoying you by printing "Time has been changed" every 5
  seconds to the system log.

Instead of doing in-kernel time adjustments offload the work to an
NTP client by exposing TimeSync messages as a PTP device. Users may now
decide what they want to use as a source.

Changes since v3:
- Minor style changes [Stephen Hemminger]
- Added a comment explaining why we don't fail the driver registration
  when ptp_clock_register() fails [Thomas Gleixner]
- Add Thomas' A-b to PATCH1

Vitaly Kuznetsov (2):
  hv_util: switch to using timespec64
  hv_utils: implement Hyper-V PTP source

 drivers/hv/hv_util.c | 146 ++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 120 insertions(+), 26 deletions(-)

-- 
2.9.3