ixgbe: Prevent u8 wrapping of ITR value to something less than 10us

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.

CC: stable@vger.kernel.org
Fixes: b4ded8327fea ("ixgbe: Update adaptive ITR algorithm")
Reported-by: Gregg Leventhal <gleventhal@janestreet.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 7882148..77ca900 100644 (file)
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -2621,7 +2621,7 @@ adjust_by_size:
                /* 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 @@ adjust_by_size:
        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;