net: ena: improve latency by disabling adaptive interrupt moderation by default

BugLink: https://bugs.launchpad.net/bugs/1850175

Adaptive interrupt moderation was erroneously enabled by default
in the driver.

In case the device supports adaptive interrupt moderation it will
be automatically used, which may potentially increase latency.

The adaptive moderation can be enabled from ethtool command in
case the feature is supported by the device.

Fixes: 1738cd3e ("net: ena: Add a driver for Amazon Elastic Network Adapters (ENA)")
Signed-off-by: Guy Tzalik <gtzalik@amazon.com>
Signed-off-by: Sameeh Jubran <sameehj@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 78cb421d)
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Khaled Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/net/ethernet/amazon/ena/ena_com.c

@@ -2801,7 +2801,11 @@ int ena_com_init_interrupt_moderation(struct ena_com_dev *ena_dev)
 	/* if moderation is supported by device we set adaptive moderation */
 	delay_resolution = get_resp.u.intr_moderation.intr_delay_resolution;
 	ena_com_update_intr_delay_resolution(ena_dev, delay_resolution);
-	ena_com_enable_adaptive_moderation(ena_dev);
+
+	/* Disable adaptive moderation by default - can be enabled from
+	 * ethtool
+	 */
+	ena_com_disable_adaptive_moderation(ena_dev);
 
 	return 0;
 err: