ixgbe: enable extremely low latency

82598/82599 can support EITR == 0, which allows for the
absolutely lowest latency setting in the hardware.  This disables
writeback batching and anything else that relies upon a delayed
interrupt. This patch enables the feature of "override" when a
user sets rx-usecs to zero, the driver will respect that setting
over using RSC, and automatically disable RSC.  If rx-usecs is
used to set the EITR value to 0, then the driver should disable
LRO (aka RSC) internally until EITR is set to non-zero again.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/net/ixgbe/ixgbe_main.c b/drivers/net/ixgbe/ixgbe_main.c
index 32781b3f8964..0c4ca6822b70 100644
--- a/drivers/net/ixgbe/ixgbe_main.c
+++ b/drivers/net/ixgbe/ixgbe_main.c
@@ -1190,6 +1190,15 @@ void ixgbe_write_eitr(struct ixgbe_q_vector *q_vector)
                 itr_reg |= (itr_reg << 16);
         } else if (adapter->hw.mac.type == ixgbe_mac_82599EB) {
                 /*
+                 * 82599 can support a value of zero, so allow it for
+                 * max interrupt rate, but there is an errata where it can
+                 * not be zero with RSC
+                 */
+                if (itr_reg == 8 &&
+                    !(adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED))
+                        itr_reg = 0;
+
+                /*
                  * set the WDIS bit to not clear the timer bits and cause an
                  * immediate assertion of the interrupt
                  */