[Intel-wired-lan] [net-queue PATCH] ixgbe: Prevent u8 wrapping of ITR value to something less than 10us

[Alexander Duyck]

From: Alexander Duyck <alexander.h.duyck at linux.intel.com>

There were a couple cases where the ITR value generated via the adaptive
ITR scheme could exceed 126. This resulted in the value becoming either 0
or something less than 10. Switching back and forth between a value less
than 10 and a value greater than 10 can cause issues as certain hardware
features such as RSC to not function well when the ITR value has dropped
that low.

Reported-by: Gregg Leventhal <gleventhal at janestreet.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck at linux.intel.com>
---
 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 5fa585dfddf6..097e6dfbf65a 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -2621,7 +2621,7 @@ static void ixgbe_update_itr(struct ixgbe_q_vector *q_vector,
 		/* 16K ints/sec to 9.2K ints/sec */
 		avg_wire_size *= 15;
 		avg_wire_size += 11452;
-	} else if (avg_wire_size <= 1980) {
+	} else if (avg_wire_size < 1968) {
 		/* 9.2K ints/sec to 8K ints/sec */
 		avg_wire_size *= 5;
 		avg_wire_size += 22420;
@@ -2654,6 +2654,8 @@ static void ixgbe_update_itr(struct ixgbe_q_vector *q_vector,
 	case IXGBE_LINK_SPEED_2_5GB_FULL:
 	case IXGBE_LINK_SPEED_1GB_FULL:
 	case IXGBE_LINK_SPEED_10_FULL:
+		if (avg_wire_size > 8064)
+			avg_wire_size = 8064;
 		itr += DIV_ROUND_UP(avg_wire_size,
 				    IXGBE_ITR_ADAPTIVE_MIN_INC * 64) *
 		       IXGBE_ITR_ADAPTIVE_MIN_INC;