From mboxrd@z Thu Jan 1 00:00:00 1970 From: Miroslav Lichvar Subject: [PATCH v2 net] igb: shorten maximum PHC timecounter update interval Date: Fri, 26 Oct 2018 19:13:00 +0200 Message-ID: <20181026171300.12720-1-mlichvar@redhat.com> Cc: intel-wired-lan@lists.osuosl.org, Miroslav Lichvar , Jacob Keller , Richard Cochran , Thomas Gleixner To: netdev@vger.kernel.org Return-path: Received: from mx1.redhat.com ([209.132.183.28]:24944 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726501AbeJ0Buv (ORCPT ); Fri, 26 Oct 2018 21:50:51 -0400 Sender: netdev-owner@vger.kernel.org List-ID: 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. Cc: Jacob Keller Cc: Richard Cochran Cc: Thomas Gleixner Signed-off-by: Miroslav Lichvar --- 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