igb: add statistic indicating number of skipped Tx timestamps

The igb driver can only handle one Tx timestamp request at a time.
This means it is possible for an application timestamp request to be
ignored.

There is no easy way for an administrator to determine if this occurred.
Add a new statistic which tracks this, tx_hwtstamp_skipped.
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igb/igb.h

@@ -563,6 +563,7 @@ struct igb_adapter {
 	struct cyclecounter cc;
 	struct timecounter tc;
 	u32 tx_hwtstamp_timeouts;
+	u32 tx_hwtstamp_skipped;
 	u32 rx_hwtstamp_cleared;
 	bool pps_sys_wrap_on;
 

drivers/net/ethernet/intel/igb/igb_ethtool.c

@@ -90,6 +90,7 @@ static const struct igb_stats igb_gstrings_stats[] = {
 	IGB_STAT("os2bmc_tx_by_host", stats.o2bspc),
 	IGB_STAT("os2bmc_rx_by_host", stats.b2ogprc),
 	IGB_STAT("tx_hwtstamp_timeouts", tx_hwtstamp_timeouts),
+	IGB_STAT("tx_hwtstamp_skipped", tx_hwtstamp_skipped),
 	IGB_STAT("rx_hwtstamp_cleared", rx_hwtstamp_cleared),
 };
 

drivers/net/ethernet/intel/igb/igb_main.c

@@ -5388,6 +5388,8 @@ netdev_tx_t igb_xmit_frame_ring(struct sk_buff *skb,
 			adapter->ptp_tx_start = jiffies;
 			if (adapter->hw.mac.type == e1000_82576)
 				schedule_work(&adapter->ptp_tx_work);
+		} else {
+			adapter->tx_hwtstamp_skipped++;
 		}
 	}