netdev - Re: [PATCH v2 net] igb: shorten maximum PHC timecounter update interval

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Date:   Tue, 30 Oct 2018 19:30:56 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Miroslav Lichvar <mlichvar@...hat.com>
Cc:     netdev@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
        Jacob Keller <jacob.e.keller@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 net] igb: shorten maximum PHC timecounter update
 interval

On Fri, Oct 26, 2018 at 07:13:00PM +0200, Miroslav Lichvar wrote:
> 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 500462a9de65 ("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. Also, the
> PHC may be adjusted to run up to 6% faster than real time and the system
> clock up to 10% slower. Shorten the delay to 360 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.

Acked-by: Richard Cochran <richardcochran@...il.com>