From: Jason Gunthorpe <jgg@ziepe.ca>
To: Miroslav Lichvar <mlichvar@redhat.com>
Cc: linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
John Stultz <john.stultz@linaro.org>,
Prarit Bhargava <prarit@redhat.com>
Subject: Re: [PATCH] rtc: adapt allowed RTC update error
Date: Tue, 1 Dec 2020 12:12:24 -0400 [thread overview]
Message-ID: <20201201161224.GF5487@ziepe.ca> (raw)
In-Reply-To: <20201201143835.2054508-1-mlichvar@redhat.com>
On Tue, Dec 01, 2020 at 03:38:35PM +0100, Miroslav Lichvar wrote:
> When the system clock is marked as synchronized via adjtimex(), the
> kernel is expected to copy the system time to the RTC every 11 minutes.
>
> There are reports that it doesn't always work reliably. It seems the
> current requirement for the RTC update to happen within 5 ticks of the
> target time in some cases can consistently fail for hours or even days.
>
> It is better to set the RTC with a larger error than let it drift for
> too long.
>
> Add a static variable to rtc_tv_nsec_ok() to count the checks. With each
> failed check, relax the requirement by one jiffie, and reset the counter
> when it finally succeeds. This should allow the RTC update to happen in
> a minute at most.
>
> Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: John Stultz <john.stultz@linaro.org>
> Cc: Prarit Bhargava <prarit@redhat.com>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> include/linux/rtc.h | 17 +++++++++++++----
> 1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/rtc.h b/include/linux/rtc.h
> index 22d1575e4991..8d105f10ef6a 100644
> +++ b/include/linux/rtc.h
> @@ -218,21 +218,30 @@ static inline bool rtc_tv_nsec_ok(s64 set_offset_nsec,
> struct timespec64 *to_set,
> const struct timespec64 *now)
> {
> - /* Allowed error in tv_nsec, arbitarily set to 5 jiffies in ns. */
> - const unsigned long TIME_SET_NSEC_FUZZ = TICK_NSEC * 5;
> struct timespec64 delay = {.tv_sec = 0,
> .tv_nsec = set_offset_nsec};
> + unsigned long time_set_nsec_fuzz;
> + static unsigned int attempt;
Adding a static value instide a static inline should not be done
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
Did you look at why time has become so in-accurate in your system? 5
jiffies is usually a pretty long time?
Jason
next prev parent reply other threads:[~2020-12-01 16:13 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 [this message]
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
2020-12-03 20:10 ` Jason Gunthorpe
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