i40e/i40evf: fix bug in throttle rate math

[firefly-linux-kernel-4.4.55.git] / drivers / net / ethernet / intel / i40evf / i40e_txrx.c

diff --git a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
index 597e0964c2322ccb9144455fc4896e5e736edd3d..7d98042338e01a8f9f16d64c458d2d59aea92125 100644 (file)
--- 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)