From: Alexandre Belloni <alexandre.belloni@free-electrons.com>
To: Pavel Machek <pavel@ucw.cz>
Cc: Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
Gabriel Beddingfield <gabe@nestlabs.com>,
LKML <linux-kernel@vger.kernel.org>,
Stephen Boyd <sboyd@codeaurora.org>,
Thomas Gleixner <tglx@linutronix.de>,
John Stultz <john.stultz@linaro.org>,
Alessandro Zummo <a.zummo@towertech.it>,
linux-rtc@vger.kernel.org, Guy Erb <guy@nestlabs.com>,
hharte@nestlabs.com
Subject: Re: Introduce clock precision to help time travelers was Re: Extreme time jitter with suspend/resume cycles
Date: Sat, 4 Nov 2017 16:34:15 +0100 [thread overview]
Message-ID: <20171104153415.bc6ttzfpwkkbbhsr@piout.net> (raw)
In-Reply-To: <20171018215638.GA7487@amd>
On 18/10/2017 at 23:56:38 +0200, Pavel Machek wrote:
> > Some RTCs will tell you when they lost time/time accuracy and this
> > should be properly reported by the driver. If not, this has to be
> > implemented.
>
> How is it reported to the userspace?
>
Userspace will get -EINVAL when using the RTC_RD_TIME ioctl. The kernel
also get the same error when reading the time from the RTC.
> > For anything else, it is probably the job of userspace to try to be
> > clever.
>
> Userspace would be fine with me, but as far as I can tell, there's no
> good way to do it in userspace.
>
> My proposal would be: kernel keeps accuracy for timeofday.
>
> If RTC says time is bad, accuracy is set to ~0.
>
> settimeofday sets accuracy to 0 (completely accurate).
>
> new_settimeofday gets new argument, accuracy.
>
> new_gettimofday returns accuracy, too.
>
> Does that sound sane? I'm not sure what other interfaces need to be extended.
>
> Best regards,
> Pavel
>
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
--
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
prev parent reply other threads:[~2017-11-04 15:34 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-04 16:11 Gabriel Beddingfield
2017-10-04 18:22 ` Thomas Gleixner
2017-10-04 23:10 ` Gabriel Beddingfield
2017-10-05 0:20 ` John Stultz
2017-10-05 16:46 ` Gabriel Beddingfield
2017-10-05 11:01 ` Thomas Gleixner
2017-10-05 16:47 ` Gabriel Beddingfield
2017-10-05 18:01 ` Thomas Gleixner
2017-10-05 20:51 ` Gabriel Beddingfield
2017-10-05 21:04 ` Thomas Gleixner
2017-10-05 21:12 ` Gabriel Beddingfield
2017-10-05 21:33 ` Thomas Gleixner
2017-10-05 0:16 ` John Stultz
2017-10-05 11:05 ` Thomas Gleixner
2017-10-05 14:11 ` Thomas Gleixner
2017-10-05 11:08 ` Miroslav Lichvar
2017-10-05 20:14 ` Gabriel Beddingfield
2017-10-05 21:31 ` Thomas Gleixner
2017-10-15 6:39 ` Introduce clock precision to help time travelers was " Pavel Machek
2017-10-18 20:34 ` Alan Cox
2017-10-18 21:08 ` Pavel Machek
2017-10-18 21:26 ` Alexandre Belloni
2017-10-18 21:56 ` Pavel Machek
2017-11-04 15:34 ` Alexandre Belloni [this message]
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