From: Alexandre Belloni <alexandre.belloni@bootlin.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Miroslav Lichvar <mlichvar@redhat.com>,
linux-kernel@vger.kernel.org,
John Stultz <john.stultz@linaro.org>,
Prarit Bhargava <prarit@redhat.com>,
Alessandro Zummo <a.zummo@towertech.it>,
linux-rtc@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] rtc: adapt allowed RTC update error
Date: Thu, 3 Dec 2020 17:07:53 +0100 [thread overview]
Message-ID: <20201203160753.GB7535@piout.net> (raw)
In-Reply-To: <20201203155249.GT5487@ziepe.ca>
On 03/12/2020 11:52:49-0400, Jason Gunthorpe wrote:
> On Thu, Dec 03, 2020 at 03:10:47AM +0100, Alexandre Belloni wrote:
>
> > IIRC, used in conjunction with rtc_hctosys which also adds
> > inconditionnaly 500ms this can ends up with the system time
> > being one second away from the wall clock time which NTP will take quite
> > some time to remove.
>
> I can't remember the details, but this was not the intention.
>
> As long as systohc and hctosys exist then the design goal of rtclib
> should be to provide sub-second accuracy on the round trip of time
> through the RTC.
>
> Otherwise what is the point?
>
hctosys never had a sub second accuracy because there is no way to
accurately read the rtc time without being ready to wait up to a second.
I have patches doing exactly that but I'm pretty sure nobody wants to
pay the price and have a kernel that boots significantly slower.
Especially since that would basically affect everyone since systemd
requires that hctosys is enabled.
--
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
next prev parent reply other threads:[~2020-12-03 16:08 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-01 14:38 [PATCH] rtc: adapt allowed RTC update error Miroslav Lichvar
2020-12-01 16:12 ` Jason Gunthorpe
2020-12-01 17:14 ` Miroslav Lichvar
2020-12-01 17:35 ` Jason Gunthorpe
2020-12-02 10:01 ` [PATCHv2] " Miroslav Lichvar
2020-12-02 13:44 ` [PATCH] " Thomas Gleixner
2020-12-02 15:07 ` Miroslav Lichvar
2020-12-02 15:36 ` Miroslav Lichvar
2020-12-02 18:36 ` Thomas Gleixner
2020-12-02 16:27 ` Jason Gunthorpe
2020-12-02 19:21 ` Thomas Gleixner
2020-12-02 20:54 ` Jason Gunthorpe
2020-12-02 22:08 ` Thomas Gleixner
2020-12-02 23:03 ` Jason Gunthorpe
2020-12-03 1:14 ` Thomas Gleixner
2020-12-03 2:04 ` Jason Gunthorpe
2020-12-03 2:10 ` Alexandre Belloni
2020-12-03 15:39 ` Thomas Gleixner
2020-12-03 16:16 ` Jason Gunthorpe
2020-12-03 21:05 ` Thomas Gleixner
2020-12-03 21:31 ` Thomas Gleixner
2020-12-03 22:36 ` Jason Gunthorpe
2020-12-04 13:02 ` Thomas Gleixner
2020-12-04 14:08 ` Jason Gunthorpe
2020-12-04 14:37 ` Alexandre Belloni
2020-12-04 14:46 ` Jason Gunthorpe
2020-12-04 15:08 ` Alexandre Belloni
2020-12-04 15:57 ` Jason Gunthorpe
2020-12-04 16:35 ` Alexandre Belloni
2020-12-03 22:00 ` Alexandre Belloni
2020-12-04 9:34 ` Thomas Gleixner
2020-12-04 9:51 ` Alexandre Belloni
2020-12-04 10:44 ` Thomas Gleixner
2020-12-03 17:29 ` Alexandre Belloni
2020-12-03 19:52 ` Thomas Gleixner
2020-12-03 15:52 ` Jason Gunthorpe
2020-12-03 16:07 ` Alexandre Belloni [this message]
2020-12-03 20:10 ` Jason Gunthorpe
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