i40e/i40evf: fix bug in throttle rate math

The driver was using a value expressed in 2us increments
for the divisor to figure out our bytes/usec values.

Fix the usecs variable to contain a value in microseconds.

Change-ID: I5c20493103c295d6f201947bb908add7040b7c41
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

2 files changed, 16 insertions, 2 deletions

diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
index 889d25d6fde2..c96e581cc2b7 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
@@ -830,6 +830,7 @@ static bool i40e_set_new_dynamic_itr(struct i40e_ring_container *rc)
         enum i40e_latency_range new_latency_range = rc->latency_range;
         u32 new_itr = rc->itr;
         int bytes_per_int;
+        int usecs;
 
         if (rc->total_packets == 0 || !rc->itr)
                 return false;
@@ -838,8 +839,14 @@ static bool i40e_set_new_dynamic_itr(struct i40e_ring_container *rc)
          *   0-10MB/s   lowest (100000 ints/s)
          *  10-20MB/s   low    (20000 ints/s)
          *  20-1249MB/s bulk   (8000 ints/s)
+         *
+         * The math works out because the divisor is in 10^(-6) which
+         * turns the bytes/us input value into MB/s values, but
+         * make sure to use usecs, as the register values written
+         * are in 2 usec increments in the ITR registers.
          */
-        bytes_per_int = rc->total_bytes / rc->itr;
+        usecs = (rc->itr << 1);
+        bytes_per_int = rc->total_bytes / usecs;
         switch (new_latency_range) {
         case I40E_LOWEST_LATENCY:
                 if (bytes_per_int > 10)
diff --git a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
index 597e0964c232..7d98042338e0 100644
--- a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
@@ -333,6 +333,7 @@ static bool i40e_set_new_dynamic_itr(struct i40e_ring_container *rc)
         enum i40e_latency_range new_latency_range = rc->latency_range;
         u32 new_itr = rc->itr;
         int bytes_per_int;
+        int usecs;
 
         if (rc->total_packets == 0 || !rc->itr)
                 return false;
@@ -341,8 +342,14 @@ static bool i40e_set_new_dynamic_itr(struct i40e_ring_container *rc)
          *   0-10MB/s   lowest (100000 ints/s)
          *  10-20MB/s   low    (20000 ints/s)
          *  20-1249MB/s bulk   (8000 ints/s)
+         *
+         * The math works out because the divisor is in 10^(-6) which
+         * turns the bytes/us input value into MB/s values, but
+         * make sure to use usecs, as the register values written
+         * are in 2 usec increments in the ITR registers.
          */
-        bytes_per_int = rc->total_bytes / rc->itr;
+        usecs = (rc->itr << 1);
+        bytes_per_int = rc->total_bytes / usecs;
         switch (new_latency_range) {
         case I40E_LOWEST_LATENCY:
                 if (bytes_per_int > 10)