linux-kernel - Re: [PATCH] rtc: adapt allowed RTC update error

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Message-ID: <20201201171420.GN1900232@localhost>
Date:   Tue, 1 Dec 2020 18:14:20 +0100
From:   Miroslav Lichvar <mlichvar@...hat.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <john.stultz@...aro.org>,
        Prarit Bhargava <prarit@...hat.com>
Subject: Re: [PATCH] rtc: adapt allowed RTC update error

On Tue, Dec 01, 2020 at 12:12:24PM -0400, Jason Gunthorpe wrote:
> On Tue, Dec 01, 2020 at 03:38:35PM +0100, Miroslav Lichvar wrote:
> > +	unsigned long time_set_nsec_fuzz;
> > +	static unsigned int attempt;
> 
> Adding a static value instide a static inline should not be done

Well, grepping through the other header files in include/linux, this
would not be the first case.

> I'm not sure using a static like this is the best idea anyhow, if you
> want something like this it should be per-rtc, not global

If there are multiple RTCs, are they all updated in this 11-minute
sync?

> Did you look at why time has become so in-accurate in your system? 5
> jiffies is usually a pretty long time?

I found no good explanation. It seems to depend on what system is
doing, if it's idle, etc. I suspect it's a property of the workqueues
that they cannot generally guarantee the jobs to run exactly on time.
I tried switching to the non-power-efficient and high priority
workqueues and it didn't seem to make a big difference.

-- 
Miroslav Lichvar