linux-kernel - [PATCH v5 0/3] hv_util: adjust system time smoothly

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Date:   Mon, 30 Jan 2017 12:07:13 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     devel@...uxdriverproject.org
Cc:     linux-kernel@...r.kernel.org,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alex Ng <alexng@...rosoft.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Olaf Hering <olaf@...fle.de>,
        Richard Cochran <richardcochran@...il.com>
Subject: [PATCH v5 0/3] 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 v4:
- Rebase to the current char-misc-next tree [K. Y.]
- Drop const qualifier from ptp_hyperv_info [kbuild test robot]
- Implement .getcrosststamp() callback [Radim Krcmar]

Vitaly Kuznetsov (3):
  hv_util: switch to using timespec64
  hv: export current Hyper-V clocksource
  hv_utils: implement Hyper-V PTP source

 arch/x86/hyperv/hv_init.c       |  13 ++-
 arch/x86/include/asm/mshyperv.h |   3 +
 drivers/hv/hv_util.c            | 183 +++++++++++++++++++++++++++++++++-------
 3 files changed, 166 insertions(+), 33 deletions(-)

-- 
2.9.3