ethtool: Add support for configuring tx_push_buf_len

This attribute, which is part of ethtool's ring param configuration
allows the user to specify the maximum number of the packet's payload
that can be written directly to the device.

Example usage:
    # ethtool -G [interface] tx-push-buf-len [number of bytes]

Co-developed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Shay Agroskin <shayagr@amazon.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 31 insertions, 16 deletions

diff --git a/Documentation/networking/ethtool-netlink.rst b/Documentation/networking/ethtool-netlink.rst
index e1bc6186d7ea..cd0973d4ba01 100644
--- a/Documentation/networking/ethtool-netlink.rst
+++ b/Documentation/networking/ethtool-netlink.rst
@@ -860,22 +860,24 @@ Request contents:
 
 Kernel response contents:
 
-  ====================================  ======  ===========================
-  ``ETHTOOL_A_RINGS_HEADER``            nested  reply header
-  ``ETHTOOL_A_RINGS_RX_MAX``            u32     max size of RX ring
-  ``ETHTOOL_A_RINGS_RX_MINI_MAX``       u32     max size of RX mini ring
-  ``ETHTOOL_A_RINGS_RX_JUMBO_MAX``      u32     max size of RX jumbo ring
-  ``ETHTOOL_A_RINGS_TX_MAX``            u32     max size of TX ring
-  ``ETHTOOL_A_RINGS_RX``                u32     size of RX ring
-  ``ETHTOOL_A_RINGS_RX_MINI``           u32     size of RX mini ring
-  ``ETHTOOL_A_RINGS_RX_JUMBO``          u32     size of RX jumbo ring
-  ``ETHTOOL_A_RINGS_TX``                u32     size of TX ring
-  ``ETHTOOL_A_RINGS_RX_BUF_LEN``        u32     size of buffers on the ring
-  ``ETHTOOL_A_RINGS_TCP_DATA_SPLIT``    u8      TCP header / data split
-  ``ETHTOOL_A_RINGS_CQE_SIZE``          u32     Size of TX/RX CQE
-  ``ETHTOOL_A_RINGS_TX_PUSH``           u8      flag of TX Push mode
-  ``ETHTOOL_A_RINGS_RX_PUSH``           u8      flag of RX Push mode
-  ====================================  ======  ===========================
+  =======================================   ======  ===========================
+  ``ETHTOOL_A_RINGS_HEADER``                nested  reply header
+  ``ETHTOOL_A_RINGS_RX_MAX``                u32     max size of RX ring
+  ``ETHTOOL_A_RINGS_RX_MINI_MAX``           u32     max size of RX mini ring
+  ``ETHTOOL_A_RINGS_RX_JUMBO_MAX``          u32     max size of RX jumbo ring
+  ``ETHTOOL_A_RINGS_TX_MAX``                u32     max size of TX ring
+  ``ETHTOOL_A_RINGS_RX``                    u32     size of RX ring
+  ``ETHTOOL_A_RINGS_RX_MINI``               u32     size of RX mini ring
+  ``ETHTOOL_A_RINGS_RX_JUMBO``              u32     size of RX jumbo ring
+  ``ETHTOOL_A_RINGS_TX``                    u32     size of TX ring
+  ``ETHTOOL_A_RINGS_RX_BUF_LEN``            u32     size of buffers on the ring
+  ``ETHTOOL_A_RINGS_TCP_DATA_SPLIT``        u8      TCP header / data split
+  ``ETHTOOL_A_RINGS_CQE_SIZE``              u32     Size of TX/RX CQE
+  ``ETHTOOL_A_RINGS_TX_PUSH``               u8      flag of TX Push mode
+  ``ETHTOOL_A_RINGS_RX_PUSH``               u8      flag of RX Push mode
+  ``ETHTOOL_A_RINGS_TX_PUSH_BUF_LEN``       u32     size of TX push buffer
+  ``ETHTOOL_A_RINGS_TX_PUSH_BUF_LEN_MAX``   u32     max size of TX push buffer
+  =======================================   ======  ===========================
 
 ``ETHTOOL_A_RINGS_TCP_DATA_SPLIT`` indicates whether the device is usable with
 page-flipping TCP zero-copy receive (``getsockopt(TCP_ZEROCOPY_RECEIVE)``).
@@ -891,6 +893,18 @@ through MMIO writes, thus reducing the latency. However, enabling this feature
 may increase the CPU cost. Drivers may enforce additional per-packet
 eligibility checks (e.g. on packet size).
 
+``ETHTOOL_A_RINGS_TX_PUSH_BUF_LEN`` specifies the maximum number of bytes of a
+transmitted packet a driver can push directly to the underlying device
+('push' mode). Pushing some of the payload bytes to the device has the
+advantages of reducing latency for small packets by avoiding DMA mapping (same
+as ``ETHTOOL_A_RINGS_TX_PUSH`` parameter) as well as allowing the underlying
+device to process packet headers ahead of fetching its payload.
+This can help the device to make fast actions based on the packet's headers.
+This is similar to the "tx-copybreak" parameter, which copies the packet to a
+preallocated DMA memory area instead of mapping new memory. However,
+tx-push-buff parameter copies the packet directly to the device to allow the
+device to take faster actions on the packet.
+
 RINGS_SET
 =========
 
@@ -908,6 +922,7 @@ Request contents:
   ``ETHTOOL_A_RINGS_CQE_SIZE``          u32     Size of TX/RX CQE
   ``ETHTOOL_A_RINGS_TX_PUSH``           u8      flag of TX Push mode
   ``ETHTOOL_A_RINGS_RX_PUSH``           u8      flag of RX Push mode
+  ``ETHTOOL_A_RINGS_TX_PUSH_BUF_LEN``   u32     size of TX push buffer
   ====================================  ======  ===========================
 
 Kernel checks that requested ring sizes do not exceed limits reported by