RFC Power-optimized RX for Ethernet devices

This patchset proposes a simple API for Ethernet drivers to cause the CPU to enter a power-optimized state while waiting for packets to arrive, along with a set of (hopefully generic) intrinsics that facilitate that. This is achieved through cooperation with the NIC driver that will allow us to know address of the next NIC RX ring packet descriptor, and wait for writes on it.

On IA, this is achieved through using UMONITOR/UMWAIT instructions. They are used in their raw opcode form because there is no widespread compiler support for them yet. Still, the API is made generic enough to hopefully support other architectures, if they happen to implement similar instructions.

To achieve power savings, there is a very simple mechanism
used: we're counting empty polls, and if a certain threshold is reached, we get the address of next RX ring descriptor from the NIC driver, arm the monitoring hardware, and enter a power-optimized state. We will then wake up when either a timeout happens, or a write happens (or generally whenever CPU feels like waking up - this is platform- specific), and proceed as normal. The empty poll counter is reset whenever we actually get packets, so we only go to sleep when we know nothing is going on.

Why are we putting it into ethdev as opposed to leaving this up to the application? Our customers specifically requested a way to do it wit minimal changes to the application code. The current approach allows to just flip a switch and automagically have power savings.

There are certain limitations in this patchset right now:
- Currently, only 1:1 core to queue mapping is supported, meaning that each lcore must at most handle RX on a single queue
- Currently, power management is enabled per-port, not per-queue
- There is potential to greatly increase TX latency if we are buffering things, and go to sleep before sending packets
- The API is not perfect and could use some improvement and discussion
- The API doesn't extend to other device types
- The intrinsics are platform-specific, so ethdev has some platform-specific code in it
- Support was only implemented for devices using net/ixgbe, net/i40e and net/ice drivers

Hopefully this would generate enough feedback to clear a path forward!

Anatoly Burakov (6):
eal: add power management intrinsics
ethdev: add simple power management API net/ixgbe: implement power management API net/i40e: implement power management API net/ice: implement power management API app/testpmd: add command for power management on a port

 app/test-pmd/cmdline.c                        |  48 +++++++
 drivers/net/i40e/i40e_ethdev.c                |   1 +
 drivers/net/i40e/i40e_rxtx.c                  |  23 +++
 drivers/net/i40e/i40e_rxtx.h                  |   2 +
 drivers/net/ice/ice_ethdev.c                  |   1 +
 drivers/net/ice/ice_rxtx.c                    |  23 +++
 drivers/net/ice/ice_rxtx.h                    |   2 +
 drivers/net/ixgbe/ixgbe_ethdev.c              |   1 +
 drivers/net/ixgbe/ixgbe_rxtx.c                |  22 +++
 drivers/net/ixgbe/ixgbe_rxtx.h                |   2 +
 .../include/generic/rte_power_intrinsics.h    |  64 +++++++++
 lib/librte_eal/include/meson.build            |   1 +
 lib/librte_eal/x86/include/meson.build        |   1 +
 lib/librte_eal/x86/include/rte_cpuflags.h     |   1 +
 .../x86/include/rte_power_intrinsics.h        | 134 ++++++++++++++++++
 lib/librte_eal/x86/rte_cpuflags.c             |   2 +
 lib/librte_ethdev/rte_ethdev.c                |  39 +++++
 lib/librte_ethdev/rte_ethdev.h                |  70 +++++++++
 lib/librte_ethdev/rte_ethdev_core.h           |  41 +++++-
 lib/librte_ethdev/rte_ethdev_version.map      |   4 +
 20 files changed, 480 insertions(+), 2 deletions(-)
 create mode 100644 lib/librte_eal/include/generic/rte_power_intrinsics.h
 create mode 100644 lib/librte_eal/x86/include/rte_power_intrinsics.h

2.17.1