netdev - RE: [Intel-wired-lan] [PATCH] igb: shorten maximum PHC timecounter update interval

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Date:   Sat, 20 Oct 2018 01:13:36 +0000
From:   "Brown, Aaron F" <aaron.f.brown@...el.com>
To:     Miroslav Lichvar <mlichvar@...hat.com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Richard Cochran <richardcochran@...il.com>
Subject: RE: [Intel-wired-lan] [PATCH] igb: shorten maximum PHC timecounter
 update interval

> From: Intel-wired-lan [mailto:intel-wired-lan-bounces@...osl.org] On
> Behalf Of Miroslav Lichvar
> Sent: Friday, October 12, 2018 4:14 AM
> To: intel-wired-lan@...ts.osuosl.org; netdev@...r.kernel.org
> Cc: Thomas Gleixner <tglx@...utronix.de>; Richard Cochran
> <richardcochran@...il.com>
> Subject: [Intel-wired-lan] [PATCH] igb: shorten maximum PHC timecounter
> update interval
> 
> The timecounter needs to be updated at least once per ~550 seconds in
> order to avoid a 40-bit SYSTIM timestamp to be misinterpreted as an old
> timestamp.
> 
> Since commit 500462a9d ("timers: Switch to a non-cascading wheel"),
> scheduling of delayed work seems to be less accurate and a requested
> delay of 540 seconds may actually be longer than 550 seconds. Shorten
> the delay to 480 seconds to be sure the timecounter is updated in time.
> 
> This fixes an issue with HW timestamps on 82580/I350/I354 being off by
> ~1100 seconds for few seconds every ~9 minutes.
> 
> Cc: Jacob Keller <jacob.e.keller@...el.com>
> Cc: Richard Cochran <richardcochran@...il.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Miroslav Lichvar <mlichvar@...hat.com>
> ---
>  drivers/net/ethernet/intel/igb/igb_ptp.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 

Tested-by: Aaron Brown <aaron.f.brown@...el.com>