This document describes the tunable parameters of the Chelsio TCP Offload
Module.  These parameters can be found under /proc/sys/toe/toe?_tom/, where
'?' is the number of the TOE device to be configured, e.g., toe0.  The current
values of the parameters can be read by 'cat'ing the corresponding file, and
can be modified by writing the new value to the files, e.g., using echo(1).

- max_host_sndbuf: A connection's send buffer is divided in two parts, one
  residing in on-card memory and the rest in the host's RAM.  This parameter
  determines the size of the latter part (max_tx_pages, described below,
  determines the first part).  The RAM portion of the send buffer acts as a
  staging area for data to be shipped to the TOE and in general needs to be
  only modestly sized.  The default value is 32K.

- max_tx_pages: This determines the maximum number of on-chip TX memory pages
  that can be given to each connection.  Together with max_host_sndbuf
  (described above) this determines the total send buffer size.  The system
  will automatically allocate pages to connections so that no connection gets
  more than max_tx_pages but under memory pressure a connection can have
  significantly fewer pages.  The minimum value is 2 pages and this is also the
  default.

- tx_hold_thres: This parameter is used to decide whether a partially filled
  TX buffer should be immediately forwarded to the TOE or whether it should be
  kept to allow more data to accumulate.  Forwarding immediately may be
  beneficial for latency but waiting to build fuller buffers reduces the
  number of transfers between the host and the TOE and improves CPU
  utilization.  A partially filled buffer is immediately forwarded if the
  number of unacknowledged data for the connection is less than tx_hold_thres.
  The default value is 0.

- rx_credit_thres: Determines how many RX credits (number of bytes read since
  the previous credit return) must have accumulated for a connection before
  we return them to the TOE.  The default is 4K.

- min_newconn_tx_pages: This is the number of free TX pages that must exist at
  the time a connection is considered for offloading in order for it to be
  offloaded.  This parameter is part of the TOE's admission control and
  defaults to 16.  A value of 0 effectively disables this test.

- auto_passv_open: If set this enables AUTO mode for passive opens.  It
  defaults to 0.

- mss: Determines the maximum amount of payload shipped to the TOE in each
  packet.  It defaults to the maximum allowed by the TOE configuration,
  usually 16K.

- del_ack: Determines whether delayed ACK is enabled.  Defaults to 1 (on) and
  changing it affects only new connections.  Note that turning off delayed
  ACKs can be detrimental to performance if communicating with NICs.

- max_conn: Maximum number of offloaded connections (excludes listeners).  At
  the moment this limit is considered only during active opens.  This
  parameter is part of the TOE's admission control and defaults to -1,
  which is unlimited.

- soft_backlog_limit: If 0 (default) a listening socket's accept queue limit is
  hard and any connections established when the accept queue is full are reset.
  In this mode new connection attempts are accepted as long as there is space
  in the SYN queue, regardless of the state of the accept queue at the time.
  If 1 the limit is soft and established connections will be added to the
  accept queue even if they overflow it, however new connection attempts will
  be accepted only if the accept queue is under its limit.

- tx_lease_time: The time in milliseconds that a connection is granted
  uninterrupted use of newly allocated TX pages (assuming it has data to
  transmit continously during that time).  This determines the quantum of the
  TX page scheduler.  It defaults to 10.