From: "Joel Daniels" <jdaniels@sent.com>
To: "Alexandre Belloni" <alexandre.belloni@bootlin.com>,
"Thomas Gleixner" <tglx@linutronix.de>
Cc: "John Stultz" <john.stultz@linaro.org>,
"Stephen Boyd" <sboyd@kernel.org>,
linux-kernel@vger.kernel.org,
"Alessandro Zummo" <a.zummo@towertech.it>,
linux-rtc@vger.kernel.org, x86@kernel.org
Subject: Re: Time keeping while suspended in the presence of persistent clock drift
Date: Wed, 15 Dec 2021 15:05:01 -0700 [thread overview]
Message-ID: <5fb8b880-8fea-4e53-a00c-994bf4890f8a@www.fastmail.com> (raw)
In-Reply-To: <YbphWpMl7W0Qzs+d@piout.net>
>> > I would like to provide a way for user space to inform the kernel
>> > that the persistent clock drifts so it can make a corresponding
>> > adjustment when resuming from a long suspend period.
>> >
>> > In my use case it would be enough for me to set this parameter on
>> > boot. In use cases with continuous network access, NTP daemons
>> > could be enhanced to periodically update this parameter with the
>> > daemon's best estimate of the persistent clock drift.
>>
>> That needs some thought. The RTC people (cc'ed now) might have opionions
>> on that.
>>
>
> The RTC subsystem already has two interfaces to correct the drift of an
> RTC. However, this is currently limited to RTC that have hardware
> support for this feature. I guess we could had software emulation of the
> feature to be able to correct for any RTCs but this will raise many
> design questions, like how often the correction has to happen, what to
> do with RTC that have a counter that doesn't reset when setting their
> time, etc...
>
> I guess this would be able to solve your particular issue has you will
> need a mechanism to handle when you overshoot the regular correction
> timer.
>
> However, everything falls down once the machine is turned off, making
> the whole effort moot...
Today two mechanism are regularly used to correct for rtc drift while
the machine is powered off: the hwclock program and chronyd with the
"-s" option. They both rely on the RTC running at the same rate when
the machine is on or off. So I agree with you that trying to emulate
hardware RTC drift correction in software is not going to work well.
prev parent reply other threads:[~2021-12-15 22:05 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <5af5d2a5-767c-d313-3be6-cb6f426f1980@sent.com>
[not found] ` <b074f506-2568-4506-9557-4a9bc9cbea83@www.fastmail.com>
[not found] ` <87wnkbuuuz.ffs@tglx>
[not found] ` <4bb238e1-e8fa-44e6-9f5e-d047d1d4a892@www.fastmail.com>
2021-12-14 13:57 ` Time keeping while suspended in the presence of persistent clock drift Thomas Gleixner
2021-12-14 17:43 ` Joel Daniels
2021-12-15 21:06 ` John Stultz
2021-12-15 21:32 ` Alexandre Belloni
2021-12-15 22:02 ` John Stultz
2021-12-15 22:33 ` Thomas Gleixner
2021-12-15 23:10 ` John Stultz
2021-12-15 22:42 ` Joel Daniels
2021-12-15 23:26 ` John Stultz
2021-12-15 23:36 ` Alexandre Belloni
2021-12-16 0:09 ` Joel Daniels
2021-12-15 23:28 ` Alexandre Belloni
2021-12-15 21:42 ` Alexandre Belloni
2021-12-15 22:05 ` Joel Daniels [this message]
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