From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: devel@linuxdriverproject.org
Cc: linux-kernel@vger.kernel.org,
"K. Y. Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
John Stultz <john.stultz@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
Alex Ng <alexng@microsoft.com>
Subject: [PATCH 0/4] hv_util: adjust system time smoothly
Date: Mon, 2 Jan 2017 20:41:10 +0100 [thread overview]
Message-ID: <20170102194114.657-1-vkuznets@redhat.com> (raw)
(First, I have to admit I'm not a timekeeping expert ...)
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.
With this series I suggest to use do_adjtimex() to adjust time. My tests
show that such method gives equally good time convergence but avoids all
the drawbacks described above.
Vitaly Kuznetsov (4):
timekeeping: export do_adjtimex() to modules
hv_util: switch to using timespec64
hv_util: use do_adjtimex() to update system time
hv_util: improve time adjustment accuracy by disabling interrupts
drivers/hv/hv_util.c | 33 +++++++++++++++++++++++++++++----
kernel/time/timekeeping.c | 1 +
2 files changed, 30 insertions(+), 4 deletions(-)
--
2.9.3
next reply other threads:[~2017-01-02 19:42 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-02 19:41 Vitaly Kuznetsov [this message]
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
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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