e1000/e1000e: implement a simple interrupt moderation

Back before e1000-7.3.20, the e1000 driver had a simple algorithm that
managed interrupt moderation.  The driver was updated in 7.3.20 to
have the new "adaptive" interrupt moderation but we have customer
requests to redeploy the old way as an option.  This patch adds the
old functionality back.  The new functionality can be enabled via
module parameter or at runtime via ethtool.
Module parameter: (InterruptThrottleRate=4) to use this new
moderation method.
Ethtool method: ethtool -C ethX rx-usecs 4

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 1 deletions

diff --git a/drivers/net/e1000e/netdev.c b/drivers/net/e1000e/netdev.c
index 478c34a47d18..c5f65a29865a 100644
--- a/drivers/net/e1000e/netdev.c
+++ b/drivers/net/e1000e/netdev.c
@@ -52,7 +52,7 @@
 
 #include "e1000.h"
 
-#define DRV_VERSION "1.0.2-k2"
+#define DRV_VERSION "1.0.2-k4"
 char e1000e_driver_name[] = "e1000e";
 const char e1000e_driver_version[] = DRV_VERSION;
 
@@ -4070,6 +4070,22 @@ link_up:
                 }
         }
 
+        /* Simple mode for Interrupt Throttle Rate (ITR) */
+        if (adapter->itr_setting == 4) {
+                /*
+                 * Symmetric Tx/Rx gets a reduced ITR=2000;
+                 * Total asymmetrical Tx or Rx gets ITR=8000;
+                 * everyone else is between 2000-8000.
+                 */
+                u32 goc = (adapter->gotc + adapter->gorc) / 10000;
+                u32 dif = (adapter->gotc > adapter->gorc ?
+                            adapter->gotc - adapter->gorc :
+                            adapter->gorc - adapter->gotc) / 10000;
+                u32 itr = goc > 0 ? (dif * 6000 / goc + 2000) : 8000;
+
+                ew32(ITR, 1000000000 / (itr * 256));
+        }
+
         /* Cause software interrupt to ensure Rx ring is cleaned */
         if (adapter->msix_entries)
                 ew32(ICS, adapter->rx_ring->ims_val);