netdev - [net 11/14] igb: shorten maximum PHC timecounter update interval

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Date:   Wed,  7 Nov 2018 11:16:28 -0800
From:   Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:     davem@...emloft.net
Cc:     Miroslav Lichvar <mlichvar@...hat.com>, netdev@...r.kernel.org,
        nhorman@...hat.com, sassmann@...hat.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: [net 11/14] igb: shorten maximum PHC timecounter update interval

From: Miroslav Lichvar <mlichvar@...hat.com>

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: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Miroslav Lichvar <mlichvar@...hat.com>
Acked-by: Jacob Keller <jacob.e.keller@...el.com>
Acked-by: Richard Cochran <richardcochran@...il.com>
Tested-by: Aaron Brown <aaron.f.brown@...el.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
---
 drivers/net/ethernet/intel/igb/igb_ptp.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/intel/igb/igb_ptp.c b/drivers/net/ethernet/intel/igb/igb_ptp.c
index 29ced6b74d36..2b95dc9c7a6a 100644
--- a/drivers/net/ethernet/intel/igb/igb_ptp.c
+++ b/drivers/net/ethernet/intel/igb/igb_ptp.c
@@ -53,13 +53,15 @@
  *   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, so we aim for 8
- * minutes to be sure the actual interval is shorter than 9.16 minutes.
+ * 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 * 8)
+#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)
-- 
2.19.1