[PATCH 5.2 38/85] ixgbe: Prevent u8 wrapping of ITR value to something less than 10us

Greg Kroah-Hartman
2019-09-18T06:28:13Z

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

commit 377228accbbb8b9738f615d791aa803f41c067e0 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -2622,7 +2622,7 @@ 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;
@@ -2655,6 +2655,8 @@ 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;