[PATCH iwl-next v2 1/8] ixgbe: lower IXGBE_ITR_ADAPTIVE_MAX_USECS to prevent RX starvation

[Aleksandr Loktionov <aleksandr.loktionov@intel.com>]

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

At the current maximum of 126 us the minimum bulk-mode interrupt rate
is ~7936 interrupts/s.  Under sustained full-line-rate bulk RX traffic
this is low enough that descriptor ring starvation can occur before the
next interrupt fires.

Lower IXGBE_ITR_ADAPTIVE_MAX_USECS from 126 to 84 us.  This raises the
minimum rate to ~11905 interrupts/s (~12K ints/s), providing enough
headroom to drain the ring before it wraps.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
---
v1 -> v2:
 - Split from monolithic ITR cleanup patch; this patch only lowers
   IXGBE_ITR_ADAPTIVE_MAX_USECS from 126 to 84.

 drivers/net/ethernet/intel/ixgbe/ixgbe.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe.h b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
index 59a1cee4..b3f4d21 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe.h
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
@@ -473,6 +473,6 @@ static inline unsigned int ixgbe_rx_pg_order(struct ixgbe_ring *ring)
 
 #define IXGBE_ITR_ADAPTIVE_MIN_INC	2
 #define IXGBE_ITR_ADAPTIVE_MIN_USECS	10
-#define IXGBE_ITR_ADAPTIVE_MAX_USECS	126
+#define IXGBE_ITR_ADAPTIVE_MAX_USECS	84
 #define IXGBE_ITR_ADAPTIVE_LATENCY	0x80
 #define IXGBE_ITR_ADAPTIVE_BULK		0x00
-- 
2.52.0