Merge branch 'enetc-Add-adaptive-interrupt-coalescing'

Claudiu Manoil says:

====================
enetc: Add adaptive interrupt coalescing

Apart from some related cleanup patches, this set
introduces in a straightforward way the support needed
to enable and configure interrupt coalescing for ENETC.

Patch 5 introduces the support needed for configuring the
interrupt coalescing parameters and for switching between
moderated (int. coalescing) and per-packet interrupt modes.
When interrupt coalescing is enabled the Rx/Tx time
thresholds are configurable, packet thresholds are fixed.
To make this work reliably, patch 5 uses the traffic
pause procedure introduced in patch 2.

Patch 6 adds DIM (Dynamic Interrupt Moderation) to implement
adaptive coalescing based on time thresholds, for the Rx 'channel'.
On the Tx side a default optimal value is used instead, optimized for
TCP traffic over 1G and 2.5G links.  This default 'optimal' value can
be overridden anytime via 'ethtool -C tx-usecs'.

netperf -t TCP_MAERTS measurements show a significant CPU load
reduction correlated w/ reduced interrupt rates. For the
measurement results refer to the comments in patch 6.

v2: Replaced Tx DIM with predefined optimal value, giving
better results. This was also suggested by Jakub (cc).
Switched order of patches 4 and 5, for better grouping.

v3: minor cleanup/improvements
====================

Signed-off-by: David S. Miller <davem@davemloft.net>