net: poll/select low latency socket support

[mirror_ubuntu-artful-kernel.git] / Documentation / sysctl / net.txt

Documentation for /proc/sys/net/*	kernel version 2.4.0-test11-pre4
	(c) 1999		Terrehon Bowden <terrehon@pacbell.net>
				Bodo Bauer <bb@ricochet.net>
	(c) 2000		Jorge Nerin <comandante@zaralinux.com>
	(c) 2009		Shen Feng <shen@cn.fujitsu.com>

For general info and legal blurb, please look in README.

==============================================================

This file contains the documentation for the sysctl files in
/proc/sys/net and is valid for Linux kernel version 2.4.0-test11-pre4.

The interface  to  the  networking  parts  of  the  kernel  is  located  in
/proc/sys/net. The following table shows all possible subdirectories.You may
see only some of them, depending on your kernel's configuration.


Table : Subdirectories in /proc/sys/net
..............................................................................
 Directory Content             Directory  Content
 core      General parameter   appletalk  Appletalk protocol
 unix      Unix domain sockets netrom     NET/ROM
 802       E802 protocol       ax25       AX25
 ethernet  Ethernet protocol   rose       X.25 PLP layer
 ipv4      IP version 4        x25        X.25 protocol
 ipx       IPX                 token-ring IBM token ring
 bridge    Bridging            decnet     DEC net
 ipv6      IP version 6        tipc       TIPC
..............................................................................

1. /proc/sys/net/core - Network core options
-------------------------------------------------------

bpf_jit_enable
--------------

This enables Berkeley Packet Filter Just in Time compiler.
Currently supported on x86_64 architecture, bpf_jit provides a framework
to speed packet filtering, the one used by tcpdump/libpcap for example.
Values :
	0 - disable the JIT (default value)
	1 - enable the JIT
	2 - enable the JIT and ask the compiler to emit traces on kernel log.

dev_weight
--------------

The maximum number of packets that kernel can handle on a NAPI interrupt,
it's a Per-CPU variable.
Default: 64

low_latency_read
----------------
Low latency busy poll timeout for socket reads. (needs CONFIG_NET_LL_RX_POLL)
Approximate time in us to spin waiting for packets on the device queue.
This sets the default value of the SO_LL socket option.
Can be set or overridden per socket by setting socket option SO_LL.
Recommended value is 50. May increase power usage.
Default: 0 (off)

low_latency_poll
----------------
Low latency busy poll timeout for poll and select. (needs CONFIG_NET_LL_RX_POLL)
Approximate time in us to spin waiting for packets on the device queue.
Recommended value depends on the number of sockets you poll on.
For several sockets 50, for several hundreds 100.
For more than that you probably want to use epoll.
Note that only sockets with SO_LL set will be busy polled, so you want to either
selectively set SO_LL on those sockets or set sysctl.net.low_latency_read globally.
May increase power usage.
Default: 0 (off)

rmem_default
------------

The default setting of the socket receive buffer in bytes.

rmem_max
--------

The maximum receive socket buffer size in bytes.

wmem_default
------------

The default setting (in bytes) of the socket send buffer.

wmem_max
--------

The maximum send socket buffer size in bytes.

message_burst and message_cost
------------------------------

These parameters  are used to limit the warning messages written to the kernel
log from  the  networking  code.  They  enforce  a  rate  limit  to  make  a
denial-of-service attack  impossible. A higher message_cost factor, results in
fewer messages that will be written. Message_burst controls when messages will
be dropped.  The  default  settings  limit  warning messages to one every five
seconds.

warnings
--------

This controls console messages from the networking stack that can occur because
of problems on the network like duplicate address or bad checksums. Normally,
this should be enabled, but if the problem persists the messages can be
disabled.

netdev_budget
-------------

Maximum number of packets taken from all interfaces in one polling cycle (NAPI
poll). In one polling cycle interfaces which are registered to polling are
probed in a round-robin manner.

netdev_max_backlog
------------------

Maximum number  of  packets,  queued  on  the  INPUT  side, when the interface
receives packets faster than kernel can process them.

netdev_tstamp_prequeue
----------------------

If set to 0, RX packet timestamps can be sampled after RPS processing, when
the target CPU processes packets. It might give some delay on timestamps, but
permit to distribute the load on several cpus.

If set to 1 (default), timestamps are sampled as soon as possible, before
queueing.

optmem_max
----------

Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence
of struct cmsghdr structures with appended data.

2. /proc/sys/net/unix - Parameters for Unix domain sockets
-------------------------------------------------------

There is only one file in this directory.
unix_dgram_qlen limits the max number of datagrams queued in Unix domain
socket's buffer. It will not take effect unless PF_UNIX flag is specified.


3. /proc/sys/net/ipv4 - IPV4 settings
-------------------------------------------------------
Please see: Documentation/networking/ip-sysctl.txt and ipvs-sysctl.txt for
descriptions of these entries.


4. Appletalk
-------------------------------------------------------

The /proc/sys/net/appletalk  directory  holds the Appletalk configuration data
when Appletalk is loaded. The configurable parameters are:

aarp-expiry-time
----------------

The amount  of  time  we keep an ARP entry before expiring it. Used to age out
old hosts.

aarp-resolve-time
-----------------

The amount of time we will spend trying to resolve an Appletalk address.

aarp-retransmit-limit
---------------------

The number of times we will retransmit a query before giving up.

aarp-tick-time
--------------

Controls the rate at which expires are checked.

The directory  /proc/net/appletalk  holds the list of active Appletalk sockets
on a machine.

The fields  indicate  the DDP type, the local address (in network:node format)
the remote  address,  the  size of the transmit pending queue, the size of the
received queue  (bytes waiting for applications to read) the state and the uid
owning the socket.

/proc/net/atalk_iface lists  all  the  interfaces  configured for appletalk.It
shows the  name  of the interface, its Appletalk address, the network range on
that address  (or  network number for phase 1 networks), and the status of the
interface.

/proc/net/atalk_route lists  each  known  network  route.  It lists the target
(network) that the route leads to, the router (may be directly connected), the
route flags, and the device the route is using.


5. IPX
-------------------------------------------------------

The IPX protocol has no tunable values in proc/sys/net.

The IPX  protocol  does,  however,  provide  proc/net/ipx. This lists each IPX
socket giving  the  local  and  remote  addresses  in  Novell  format (that is
network:node:port). In  accordance  with  the  strange  Novell  tradition,
everything but the port is in hex. Not_Connected is displayed for sockets that
are not  tied to a specific remote address. The Tx and Rx queue sizes indicate
the number  of  bytes  pending  for  transmission  and  reception.  The  state
indicates the  state  the  socket  is  in and the uid is the owning uid of the
socket.

The /proc/net/ipx_interface  file lists all IPX interfaces. For each interface
it gives  the network number, the node number, and indicates if the network is
the primary  network.  It  also  indicates  which  device  it  is bound to (or
Internal for  internal  networks)  and  the  Frame  Type if appropriate. Linux
supports 802.3,  802.2,  802.2  SNAP  and DIX (Blue Book) ethernet framing for
IPX.

The /proc/net/ipx_route  table  holds  a list of IPX routes. For each route it
gives the  destination  network, the router node (or Directly) and the network
address of the router (or Connected) for internal networks.

6. TIPC
-------------------------------------------------------

The TIPC protocol now has a tunable for the receive memory, similar to the
tcp_rmem - i.e. a vector of 3 INTEGERs: (min, default, max)

    # cat /proc/sys/net/tipc/tipc_rmem
    4252725 34021800        68043600
    #

The max value is set to CONN_OVERLOAD_LIMIT, and the default and min values
are scaled (shifted) versions of that same value.  Note that the min value
is not at this point in time used in any meaningful way, but the triplet is
preserved in order to be consistent with things like tcp_rmem.