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

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Message-ID: <02874ECE860811409154E81DA85FBB5884CE4BF5@ORSMSX115.amr.corp.intel.com>
Date:   Fri, 26 Oct 2018 17:20:41 +0000
From:   "Keller, Jacob E" <jacob.e.keller@...el.com>
To:     Miroslav Lichvar <mlichvar@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        Richard Cochran <richardcochran@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: RE: [PATCH v2 net] igb: shorten maximum PHC timecounter update
 interval

> -----Original Message-----
> From: Miroslav Lichvar [mailto:mlichvar@...hat.com]
> Sent: Friday, October 26, 2018 10:13 AM
> To: netdev@...r.kernel.org
> Cc: intel-wired-lan@...ts.osuosl.org; Miroslav Lichvar <mlichvar@...hat.com>;
> Keller, Jacob E <jacob.e.keller@...el.com>; Richard Cochran
> <richardcochran@...il.com>; Thomas Gleixner <tglx@...utronix.de>
> Subject: [PATCH v2 net] 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 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: Jacob Keller <jacob.e.keller@...el.com>

> 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 | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/intel/igb/igb_ptp.c
> b/drivers/net/ethernet/intel/igb/igb_ptp.c
> index 9f4d700e09df..2b95dc9c7a6a 100644
> --- a/drivers/net/ethernet/intel/igb/igb_ptp.c
> +++ b/drivers/net/ethernet/intel/igb/igb_ptp.c
> @@ -51,9 +51,17 @@
>   *
>   * The 40 bit 82580 SYSTIM overflows every
>   *   2^40 * 10^-9 /  60  = 18.3 minutes.
> + *
> + * SYSTIM is converted to real time using a timecounter. As
> + * timecounter_cyc2time() allows old timestamps, the timecounter needs
> + * to be updated at least once per half of the SYSTIM interval.
> + * Scheduling of delayed work is not very accurate, and also the NIC
> + * clock can be adjusted to run up to 6% faster and the system clock
> + * up to 10% slower, so we aim for 6 minutes to be sure the actual
> + * interval in the NIC time is shorter than 9.16 minutes.
>   */
> 
> -#define IGB_SYSTIM_OVERFLOW_PERIOD	(HZ * 60 * 9)
> +#define IGB_SYSTIM_OVERFLOW_PERIOD	(HZ * 60 * 6)
>  #define IGB_PTP_TX_TIMEOUT		(HZ * 15)
>  #define INCPERIOD_82576			BIT(E1000_TIMINCA_16NS_SHIFT)
>  #define INCVALUE_82576_MASK
> 	GENMASK(E1000_TIMINCA_16NS_SHIFT - 1, 0)
> --
> 2.17.2